Datasets:

dvdmrs09

/

py2

like 0

signal Set handlers for asynchronous events Source code Lib signal py This module provides mechanisms to use signal handlers in Python General rules The signal signal function allows defining custom handlers to be executed when a signal is received A small number of default handlers are installed SIGPIPE is ignored so write errors on pipes and sockets can be reported as ordinary Python exceptions and SIGINT is translated into a KeyboardInterrupt exception if the parent process has not changed it A handler for a particular signal once set remains installed until it is explicitly reset Python emulates the BSD style interface regardless of the underlying implementation with the exception of the handler for SIGCHLD which follows the underlying implementation On WebAssembly platforms wasm32 emscripten and wasm32 wasi signals are emulated and therefore behave differently Several functions and signals are not available on these platforms Execution of Python signal handlers A Python signal handler does not get executed inside the low level C signal handler Instead the low level signal handler sets a flag which tells the virtual machine to execute the corresponding Python signal handler at a later point for example at the next bytecode instruction This has consequences It makes little sense to catch synchronous errors like SIGFPE or SIGSEGV that are caused by an invalid operation in C code Python will return from the signal handler to the C code which is likely to raise the same signal again causing Python to apparently hang From Python 3 3 onwards you can use the faulthandler module to report on synchronous errors A long running calculation implemented purely in C such as regular expression matching on a large body of text may run uninterrupted for an arbitrary amount of time regardless of any signals received The Python signal handlers will be called when the calculation finishes If the handler raises an exception it will be raised out of thin air in the main thread See the note below for a discussion Signals and threads Python signal handlers are always executed in the main Python thread of the main interpreter even if the signal was received in another thread This means that signals can t be used as a means of inter thread communication You can use the synchronization primitives from the threading module instead Besides only the main thread of the main interpreter is allowed to set a new signal handler Module contents Changed in version 3 5 signal SIG handler SIG_DFL SIG_IGN and sigmask SIG_BLOCK SIG_UNBLOCK SIG_SETMASK related constants listed below were turned into enums Signals Handlers and Sigmasks respectively getsignal pthread_sigmask sigpending and sigwait functions return human readable enums as Signals objects The signal module defines three enums class signal Signals enum IntEnum collection of SIG constants and the CTRL_ constants New in version 3 5 class signal Handlers enum IntEnum collection the constants SIG_DFL and SIG_IGN New in version 3 5 class signal Sigmasks enum IntEnum collection the constants SIG_BLOCK SIG_UNBLOCK and SIG_SETMASK Availability Unix See the man page sigprocmask 2 and pthread_sigmask 3 for further information New in version 3 5 The variables defined in the signal module are signal SIG_DFL This is one of two standard signal handling options it will simply perform the default function for the signal For example on most systems the default action for SIGQUIT is to dump core and exit while the default action for SIGCHLD is to simply ignore it signal SIG_IGN This is another standard signal handler which will simply ignore the given signal signal SIGABRT Abort signal from abort 3 signal SIGALRM Timer signal from alarm 2 Availability Unix signal SIGBREAK Interrupt from keyboard CTRL BREAK Availability Windows signal SIGBUS Bus error bad memory access Availability Unix signal SIGCHLD Child process stopped or terminated Availability Unix signal SIGCLD Alias to SIGCHLD Availability not macOS signal SIGCONT Continue the process if it is currently stopped Availability Unix signal SIGFPE Floating point

en

exception For example division by zero See also ZeroDivisionError is raised when the second argument of a division or modulo operation is zero signal SIGHUP Hangup detected on controlling terminal or death of controlling process Availability Unix signal SIGILL Illegal instruction signal SIGINT Interrupt from keyboard CTRL C Default action is to raise KeyboardInterrupt signal SIGKILL Kill signal It cannot be caught blocked or ignored Availability Unix signal SIGPIPE Broken pipe write to pipe with no readers Default action is to ignore the signal Availability Unix signal SIGSEGV Segmentation fault invalid memory reference signal SIGSTKFLT Stack fault on coprocessor The Linux kernel does not raise this signal it can only be raised in user space Availability Linux On architectures where the signal is available See the man page signal 7 for further information New in version 3 11 signal SIGTERM Termination signal signal SIGUSR1 User defined signal 1 Availability Unix signal SIGUSR2 User defined signal 2 Availability Unix signal SIGWINCH Window resize signal Availability Unix SIG All the signal numbers are defined symbolically For example the hangup signal is defined as signal SIGHUP the variable names are identical to the names used in C programs as found in signal h The Unix man page for signal lists the existing signals on some systems this is signal 2 on others the list is in signal 7 Note that not all systems define the same set of signal names only those names defined by the system are defined by this module signal CTRL_C_EVENT The signal corresponding to the Ctrl C keystroke event This signal can only be used with os kill Availability Windows New in version 3 2 signal CTRL_BREAK_EVENT The signal corresponding to the Ctrl Break keystroke event This signal can only be used with os kill Availability Windows New in version 3 2 signal NSIG One more than the number of the highest signal number Use valid_signals to get valid signal numbers signal ITIMER_REAL Decrements interval timer in real time and delivers SIGALRM upon expiration signal ITIMER_VIRTUAL Decrements interval timer only when the process is executing and delivers SIGVTALRM upon expiration signal ITIMER_PROF Decrements interval timer both when the process executes and when the system is executing on behalf of the process Coupled with ITIMER_VIRTUAL this timer is usually used to profile the time spent by the application in user and kernel space SIGPROF is delivered upon expiration signal SIG_BLOCK A possible value for the how parameter to pthread_sigmask indicating that signals are to be blocked New in version 3 3 signal SIG_UNBLOCK A possible value for the how parameter to pthread_sigmask indicating that signals are to be unblocked New in version 3 3 signal SIG_SETMASK A possible value for the how parameter to pthread_sigmask indicating that the signal mask is to be replaced New in version 3 3 The signal module defines one exception exception signal ItimerError Raised to signal an error from the underlying setitimer or getitimer implementation Expect this error if an invalid interval timer or a negative time is passed to setitimer This error is a subtype of OSError New in version 3 3 This error used to be a subtype of IOError which is now an alias of OSError The signal module defines the following functions signal alarm time If time is non zero this function requests that a SIGALRM signal be sent to the process in time seconds Any previously scheduled alarm is canceled only one alarm can be scheduled at any time The returned value is then the number of seconds before any previously set alarm was to have been delivered If time is zero no alarm is scheduled and any scheduled alarm is canceled If the return value is zero no alarm is currently scheduled Availability Unix See the man page alarm 2 for further information signal getsignal signalnum Return the current signal handler for the signal signalnum The returned value may be a callable Python object or one of the special values signal SIG_IGN signal SIG_DFL or None Here signal SIG_IGN means that the signal was pr

en

eviously ignored signal SIG_DFL means that the default way of handling the signal was previously in use and None means that the previous signal handler was not installed from Python signal strsignal signalnum Returns the description of signal signalnum such as Interrupt for SIGINT Returns None if signalnum has no description Raises ValueError if signalnum is invalid New in version 3 8 signal valid_signals Return the set of valid signal numbers on this platform This can be less than range 1 NSIG if some signals are reserved by the system for internal use New in version 3 8 signal pause Cause the process to sleep until a signal is received the appropriate handler will then be called Returns nothing Availability Unix See the man page signal 2 for further information See also sigwait sigwaitinfo sigtimedwait and sigpending signal raise_signal signum Sends a signal to the calling process Returns nothing New in version 3 8 signal pidfd_send_signal pidfd sig siginfo None flags 0 Send signal sig to the process referred to by file descriptor pidfd Python does not currently support the siginfo parameter it must be None The flags argument is provided for future extensions no flag values are currently defined See the pidfd_send_signal 2 man page for more information Availability Linux 5 1 New in version 3 9 signal pthread_kill thread_id signalnum Send the signal signalnum to the thread thread_id another thread in the same process as the caller The target thread can be executing any code Python or not However if the target thread is executing the Python interpreter the Python signal handlers will be executed by the main thread of the main interpreter Therefore the only point of sending a signal to a particular Python thread would be to force a running system call to fail with InterruptedError Use threading get_ident or the ident attribute of threading Thread objects to get a suitable value for thread_id If signalnum is 0 then no signal is sent but error checking is still performed this can be used to check if the target thread is still running Raises an auditing event signal pthread_kill with arguments thread_id signalnum Availability Unix See the man page pthread_kill 3 for further information See also os kill New in version 3 3 signal pthread_sigmask how mask Fetch and or change the signal mask of the calling thread The signal mask is the set of signals whose delivery is currently blocked for the caller Return the old signal mask as a set of signals The behavior of the call is dependent on the value of how as follows SIG_BLOCK The set of blocked signals is the union of the current set and the mask argument SIG_UNBLOCK The signals in mask are removed from the current set of blocked signals It is permissible to attempt to unblock a signal which is not blocked SIG_SETMASK The set of blocked signals is set to the mask argument mask is a set of signal numbers e g signal SIGINT signal SIGTERM Use valid_signals for a full mask including all signals For example signal pthread_sigmask signal SIG_BLOCK reads the signal mask of the calling thread SIGKILL and SIGSTOP cannot be blocked Availability Unix See the man page sigprocmask 2 and pthread_sigmask 3 for further information See also pause sigpending and sigwait New in version 3 3 signal setitimer which seconds interval 0 0 Sets given interval timer one of signal ITIMER_REAL signal ITIMER_VIRTUAL or signal ITIMER_PROF specified by which to fire after seconds float is accepted different from alarm and after that every interval seconds if interval is non zero The interval timer specified by which can be cleared by setting seconds to zero When an interval timer fires a signal is sent to the process The signal sent is dependent on the timer being used signal ITIMER_REAL will deliver SIGALRM signal ITIMER_VIRTUAL sends SIGVTALRM and signal ITIMER_PROF will deliver SIGPROF The old values are returned as a tuple delay interval Attempting to pass an invalid interval timer will cause an ItimerError Availability Unix signal getitimer which Returns current value of a given interval timer specified by

en

which Availability Unix signal set_wakeup_fd fd warn_on_full_buffer True Set the wakeup file descriptor to fd When a signal is received the signal number is written as a single byte into the fd This can be used by a library to wakeup a poll or select call allowing the signal to be fully processed The old wakeup fd is returned or 1 if file descriptor wakeup was not enabled If fd is 1 file descriptor wakeup is disabled If not 1 fd must be non blocking It is up to the library to remove any bytes from fd before calling poll or select again When threads are enabled this function can only be called from the main thread of the main interpreter attempting to call it from other threads will cause a ValueError exception to be raised There are two common ways to use this function In both approaches you use the fd to wake up when a signal arrives but then they differ in how they determine which signal or signals have arrived In the first approach we read the data out of the fd s buffer and the byte values give you the signal numbers This is simple but in rare cases it can run into a problem generally the fd will have a limited amount of buffer space and if too many signals arrive too quickly then the buffer may become full and some signals may be lost If you use this approach then you should set warn_on_full_buffer True which will at least cause a warning to be printed to stderr when signals are lost In the second approach we use the wakeup fd only for wakeups and ignore the actual byte values In this case all we care about is whether the fd s buffer is empty or non empty a full buffer doesn t indicate a problem at all If you use this approach then you should set warn_on_full_buffer False so that your users are not confused by spurious warning messages Changed in version 3 5 On Windows the function now also supports socket handles Changed in version 3 7 Added warn_on_full_buffer parameter signal siginterrupt signalnum flag Change system call restart behaviour if flag is False system calls will be restarted when interrupted by signal signalnum otherwise system calls will be interrupted Returns nothing Availability Unix See the man page siginterrupt 3 for further information Note that installing a signal handler with signal will reset the restart behaviour to interruptible by implicitly calling siginterrupt with a true flag value for the given signal signal signal signalnum handler Set the handler for signal signalnum to the function handler handler can be a callable Python object taking two arguments see below or one of the special values signal SIG_IGN or signal SIG_DFL The previous signal handler will be returned see the description of getsignal above See the Unix man page signal 2 for further information When threads are enabled this function can only be called from the main thread of the main interpreter attempting to call it from other threads will cause a ValueError exception to be raised The handler is called with two arguments the signal number and the current stack frame None or a frame object for a description of frame objects see the description in the type hierarchy or see the attribute descriptions in the inspect module On Windows signal can only be called with SIGABRT SIGFPE SIGILL SIGINT SIGSEGV SIGTERM or SIGBREAK A ValueError will be raised in any other case Note that not all systems define the same set of signal names an AttributeError will be raised if a signal name is not defined as SIG module level constant signal sigpending Examine the set of signals that are pending for delivery to the calling thread i e the signals which have been raised while blocked Return the set of the pending signals Availability Unix See the man page sigpending 2 for further information See also pause pthread_sigmask and sigwait New in version 3 3 signal sigwait sigset Suspend execution of the calling thread until the delivery of one of the signals specified in the signal set sigset The function accepts the signal removes it from the pending list of signals and returns the signal number Availability Unix See the man page sigwait 3 for fu

en

rther information See also pause pthread_sigmask sigpending sigwaitinfo and sigtimedwait New in version 3 3 signal sigwaitinfo sigset Suspend execution of the calling thread until the delivery of one of the signals specified in the signal set sigset The function accepts the signal and removes it from the pending list of signals If one of the signals in sigset is already pending for the calling thread the function will return immediately with information about that signal The signal handler is not called for the delivered signal The function raises an InterruptedError if it is interrupted by a signal that is not in sigset The return value is an object representing the data contained in the siginfo_t structure namely si_signo si_code si_errno si_pid si_uid si_status si_band Availability Unix See the man page sigwaitinfo 2 for further information See also pause sigwait and sigtimedwait New in version 3 3 Changed in version 3 5 The function is now retried if interrupted by a signal not in sigset and the signal handler does not raise an exception see PEP 475 for the rationale signal sigtimedwait sigset timeout Like sigwaitinfo but takes an additional timeout argument specifying a timeout If timeout is specified as 0 a poll is performed Returns None if a timeout occurs Availability Unix See the man page sigtimedwait 2 for further information See also pause sigwait and sigwaitinfo New in version 3 3 Changed in version 3 5 The function is now retried with the recomputed timeout if interrupted by a signal not in sigset and the signal handler does not raise an exception see PEP 475 for the rationale Examples Here is a minimal example program It uses the alarm function to limit the time spent waiting to open a file this is useful if the file is for a serial device that may not be turned on which would normally cause the os open to hang indefinitely The solution is to set a 5 second alarm before opening the file if the operation takes too long the alarm signal will be sent and the handler raises an exception import signal os def handler signum frame signame signal Signals signum name print f Signal handler called with signal signame signum raise OSError Couldn t open device Set the signal handler and a 5 second alarm signal signal signal SIGALRM handler signal alarm 5 This open may hang indefinitely fd os open dev ttyS0 os O_RDWR signal alarm 0 Disable the alarm Note on SIGPIPE Piping output of your program to tools like head 1 will cause a SIGPIPE signal to be sent to your process when the receiver of its standard output closes early This results in an exception like BrokenPipeError Errno 32 Broken pipe To handle this case wrap your entry point to catch this exception as follows import os import sys def main try simulate large output your code replaces this loop for x in range 10000 print y flush output here to force SIGPIPE to be triggered while inside this try block sys stdout flush except BrokenPipeError Python flushes standard streams on exit redirect remaining output to devnull to avoid another BrokenPipeError at shutdown devnull os open os devnull os O_WRONLY os dup2 devnull sys stdout fileno sys exit 1 Python exits with error code 1 on EPIPE if __name__ __main__ main Do not set SIGPIPE s disposition to SIG_DFL in order to avoid BrokenPipeError Doing that would cause your program to exit unexpectedly whenever any socket connection is interrupted while your program is still writing to it Note on Signal Handlers and Exceptions If a signal handler raises an exception the exception will be propagated to the main thread and may be raised after any bytecode instruction Most notably a KeyboardInterrupt may appear at any point during execution Most Python code including the standard library cannot be made robust against this and so a KeyboardInterrupt or any other exception resulting from a signal handler may on rare occasions put the program in an unexpected state To illustrate this issue consider the following code class SpamContext def __init__ self self lock threading Lock def __enter__ self If KeyboardInterrupt occurs here every

en

thing is fine self lock acquire If KeyboardInterrupt occurs here __exit__ will not be called KeyboardInterrupt could occur just before the function returns def __exit__ self exc_type exc_val exc_tb self lock release For many programs especially those that merely want to exit on KeyboardInterrupt this is not a problem but applications that are complex or require high reliability should avoid raising exceptions from signal handlers They should also avoid catching KeyboardInterrupt as a means of gracefully shutting down Instead they should install their own SIGINT handler Below is an example of an HTTP server that avoids KeyboardInterrupt import signal import socket from selectors import DefaultSelector EVENT_READ from http server import HTTPServer SimpleHTTPRequestHandler interrupt_read interrupt_write socket socketpair def handler signum frame print Signal handler called with signal signum interrupt_write send b 0 signal signal signal SIGINT handler def serve_forever httpd sel DefaultSelector sel register interrupt_read EVENT_READ sel register httpd EVENT_READ while True for key _ in sel select if key fileobj interrupt_read interrupt_read recv 1 return if key fileobj httpd httpd handle_request print Serving on port 8000 httpd HTTPServer 8000 SimpleHTTPRequestHandler serve_forever httpd print Shutdown

en

email headerregistry Custom Header Objects Source code Lib email headerregistry py New in version 3 6 1 Headers are represented by customized subclasses of str The particular class used to represent a given header is determined by the header_factory of the policy in effect when the headers are created This section documents the particular header_factory implemented by the email package for handling RFC 5322 compliant email messages which not only provides customized header objects for various header types but also provides an extension mechanism for applications to add their own custom header types When using any of the policy objects derived from EmailPolicy all headers are produced by HeaderRegistry and have BaseHeader as their last base class Each header class has an additional base class that is determined by the type of the header For example many headers have the class UnstructuredHeader as their other base class The specialized second class for a header is determined by the name of the header using a lookup table stored in the HeaderRegistry All of this is managed transparently for the typical application program but interfaces are provided for modifying the default behavior for use by more complex applications The sections below first document the header base classes and their attributes followed by the API for modifying the behavior of HeaderRegistry and finally the support classes used to represent the data parsed from structured headers class email headerregistry BaseHeader name value name and value are passed to BaseHeader from the header_factory call The string value of any header object is the value fully decoded to unicode This base class defines the following read only properties name The name of the header the portion of the field before the This is exactly the value passed in the header_factory call for name that is case is preserved defects A tuple of HeaderDefect instances reporting any RFC compliance problems found during parsing The email package tries to be complete about detecting compliance issues See the errors module for a discussion of the types of defects that may be reported max_count The maximum number of headers of this type that can have the same name A value of None means unlimited The BaseHeader value for this attribute is None it is expected that specialized header classes will override this value as needed BaseHeader also provides the following method which is called by the email library code and should not in general be called by application programs fold policy Return a string containing linesep characters as required to correctly fold the header according to policy A cte_type of 8bit will be treated as if it were 7bit since headers may not contain arbitrary binary data If utf8 is False non ASCII data will be RFC 2047 encoded BaseHeader by itself cannot be used to create a header object It defines a protocol that each specialized header cooperates with in order to produce the header object Specifically BaseHeader requires that the specialized class provide a classmethod named parse This method is called as follows parse string kwds kwds is a dictionary containing one pre initialized key defects defects is an empty list The parse method should append any detected defects to this list On return the kwds dictionary must contain values for at least the keys decoded and defects decoded should be the string value for the header that is the header value fully decoded to unicode The parse method should assume that string may contain content transfer encoded parts but should correctly handle all valid unicode characters as well so that it can parse un encoded header values BaseHeader s __new__ then creates the header instance and calls its init method The specialized class only needs to provide an init method if it wishes to set additional attributes beyond those provided by BaseHeader itself Such an init method should look like this def init self args kw self _myattr kw pop myattr super init args kw That is anything extra that the specialized class puts in to the kwds dictionary should be r

en

emoved and handled and the remaining contents of kw and args passed to the BaseHeader init method class email headerregistry UnstructuredHeader An unstructured header is the default type of header in RFC 5322 Any header that does not have a specified syntax is treated as unstructured The classic example of an unstructured header is the Subject header In RFC 5322 an unstructured header is a run of arbitrary text in the ASCII character set RFC 2047 however has an RFC 5322 compatible mechanism for encoding non ASCII text as ASCII characters within a header value When a value containing encoded words is passed to the constructor the UnstructuredHeader parser converts such encoded words into unicode following the RFC 2047 rules for unstructured text The parser uses heuristics to attempt to decode certain non compliant encoded words Defects are registered in such cases as well as defects for issues such as invalid characters within the encoded words or the non encoded text This header type provides no additional attributes class email headerregistry DateHeader RFC 5322 specifies a very specific format for dates within email headers The DateHeader parser recognizes that date format as well as recognizing a number of variant forms that are sometimes found in the wild This header type provides the following additional attributes datetime If the header value can be recognized as a valid date of one form or another this attribute will contain a datetime instance representing that date If the timezone of the input date is specified as 0000 indicating it is in UTC but contains no information about the source timezone then datetime will be a naive datetime If a specific timezone offset is found including 0000 then datetime will contain an aware datetime that uses datetime timezone to record the timezone offset The decoded value of the header is determined by formatting the datetime according to the RFC 5322 rules that is it is set to email utils format_datetime self datetime When creating a DateHeader value may be datetime instance This means for example that the following code is valid and does what one would expect msg Date datetime 2011 7 15 21 Because this is a naive datetime it will be interpreted as a UTC timestamp and the resulting value will have a timezone of 0000 Much more useful is to use the localtime function from the utils module msg Date utils localtime This example sets the date header to the current time and date using the current timezone offset class email headerregistry AddressHeader Address headers are one of the most complex structured header types The AddressHeader class provides a generic interface to any address header This header type provides the following additional attributes groups A tuple of Group objects encoding the addresses and groups found in the header value Addresses that are not part of a group are represented in this list as single address Groups whose display_name is None addresses A tuple of Address objects encoding all of the individual addresses from the header value If the header value contains any groups the individual addresses from the group are included in the list at the point where the group occurs in the value that is the list of addresses is flattened into a one dimensional list The decoded value of the header will have all encoded words decoded to unicode idna encoded domain names are also decoded to unicode The decoded value is set by joining the str value of the elements of the groups attribute with A list of Address and Group objects in any combination may be used to set the value of an address header Group objects whose display_name is None will be interpreted as single addresses which allows an address list to be copied with groups intact by using the list obtained from the groups attribute of the source header class email headerregistry SingleAddressHeader A subclass of AddressHeader that adds one additional attribute address The single address encoded by the header value If the header value actually contains more than one address which would be a violation of the RFC under t

en

he default policy accessing this attribute will result in a ValueError Many of the above classes also have a Unique variant for example UniqueUnstructuredHeader The only difference is that in the Unique variant max_count is set to 1 class email headerregistry MIMEVersionHeader There is really only one valid value for the MIME Version header and that is 1 0 For future proofing this header class supports other valid version numbers If a version number has a valid value per RFC 2045 then the header object will have non None values for the following attributes version The version number as a string with any whitespace and or comments removed major The major version number as an integer minor The minor version number as an integer class email headerregistry ParameterizedMIMEHeader MIME headers all start with the prefix Content Each specific header has a certain value described under the class for that header Some can also take a list of supplemental parameters which have a common format This class serves as a base for all the MIME headers that take parameters params A dictionary mapping parameter names to parameter values class email headerregistry ContentTypeHeader A ParameterizedMIMEHeader class that handles the Content Type header content_type The content type string in the form maintype subtype maintype subtype class email headerregistry ContentDispositionHeader A ParameterizedMIMEHeader class that handles the Content Disposition header content_disposition inline and attachment are the only valid values in common use class email headerregistry ContentTransferEncoding Handles the Content Transfer Encoding header cte Valid values are 7bit 8bit base64 and quoted printable See RFC 2045 for more information class email headerregistry HeaderRegistry base_class BaseHeader default_class UnstructuredHeader use_default_map True This is the factory used by EmailPolicy by default HeaderRegistry builds the class used to create a header instance dynamically using base_class and a specialized class retrieved from a registry that it holds When a given header name does not appear in the registry the class specified by default_class is used as the specialized class When use_default_map is True the default the standard mapping of header names to classes is copied in to the registry during initialization base_class is always the last class in the generated class s __bases__ list The default mappings are subject UniqueUnstructuredHeader date UniqueDateHeader resent date DateHeader orig date UniqueDateHeader sender UniqueSingleAddressHeader resent sender SingleAddressHeader to UniqueAddressHeader resent to AddressHeader cc UniqueAddressHeader resent cc AddressHeader bcc UniqueAddressHeader resent bcc AddressHeader from UniqueAddressHeader resent from AddressHeader reply to UniqueAddressHeader mime version MIMEVersionHeader content type ContentTypeHeader content disposition ContentDispositionHeader content transfer encoding ContentTransferEncodingHeader message id MessageIDHeader HeaderRegistry has the following methods map_to_type self name cls name is the name of the header to be mapped It will be converted to lower case in the registry cls is the specialized class to be used along with base_class to create the class used to instantiate headers that match name __getitem__ name Construct and return a class to handle creating a name header __call__ name value Retrieves the specialized header associated with name from the registry using default_class if name does not appear in the registry and composes it with base_class to produce a class calls the constructed class s constructor passing it the same argument list and finally returns the class instance created thereby The following classes are the classes used to represent data parsed from structured headers and can in general be used by an application program to construct structured values to assign to specific headers class email headerregistry Address display_name username domain addr_spec None The class used to represent an email address The general form of an address is display_name usernam

en

e domain or username domain where each part must conform to specific syntax rules spelled out in RFC 5322 As a convenience addr_spec can be specified instead of username and domain in which case username and domain will be parsed from the addr_spec An addr_spec must be a properly RFC quoted string if it is not Address will raise an error Unicode characters are allowed and will be property encoded when serialized However per the RFCs unicode is not allowed in the username portion of the address display_name The display name portion of the address if any with all quoting removed If the address does not have a display name this attribute will be an empty string username The username portion of the address with all quoting removed domain The domain portion of the address addr_spec The username domain portion of the address correctly quoted for use as a bare address the second form shown above This attribute is not mutable __str__ The str value of the object is the address quoted according to RFC 5322 rules but with no Content Transfer Encoding of any non ASCII characters To support SMTP RFC 5321 Address handles one special case if username and domain are both the empty string or None then the string value of the Address is class email headerregistry Group display_name None addresses None The class used to represent an address group The general form of an address group is display_name address list As a convenience for processing lists of addresses that consist of a mixture of groups and single addresses a Group may also be used to represent single addresses that are not part of a group by setting display_name to None and providing a list of the single address as addresses display_name The display_name of the group If it is None and there is exactly one Address in addresses then the Group represents a single address that is not in a group addresses A possibly empty tuple of Address objects representing the addresses in the group __str__ The str value of a Group is formatted according to RFC 5322 but with no Content Transfer Encoding of any non ASCII characters If display_name is none and there is a single Address in the addresses list the str value will be the same as the str of that single Address Footnotes 1 Originally added in 3 3 as a provisional module

en

html entities Definitions of HTML general entities Source code Lib html entities py This module defines four dictionaries html5 name2codepoint codepoint2name and entitydefs html entities html5 A dictionary that maps HTML5 named character references 1 to the equivalent Unicode character s e g html5 gt Note that the trailing semicolon is included in the name e g gt however some of the names are accepted by the standard even without the semicolon in this case the name is present with and without the See also html unescape New in version 3 3 html entities entitydefs A dictionary mapping XHTML 1 0 entity definitions to their replacement text in ISO Latin 1 html entities name2codepoint A dictionary that maps HTML4 entity names to the Unicode code points html entities codepoint2name A dictionary that maps Unicode code points to HTML4 entity names Footnotes 1 See https html spec whatwg org multipage named characters html named character references

en

Enum HOWTO An Enum is a set of symbolic names bound to unique values They are similar to global variables but they offer a more useful repr grouping type safety and a few other features They are most useful when you have a variable that can take one of a limited selection of values For example the days of the week from enum import Enum class Weekday Enum MONDAY 1 TUESDAY 2 WEDNESDAY 3 THURSDAY 4 FRIDAY 5 SATURDAY 6 SUNDAY 7 Or perhaps the RGB primary colors from enum import Enum class Color Enum RED 1 GREEN 2 BLUE 3 As you can see creating an Enum is as simple as writing a class that inherits from Enum itself Note Case of Enum MembersBecause Enums are used to represent constants and to help avoid issues with name clashes between mixin class methods attributes and enum names we strongly recommend using UPPER_CASE names for members and will be using that style in our examples Depending on the nature of the enum a member s value may or may not be important but either way that value can be used to get the corresponding member Weekday 3 Weekday WEDNESDAY 3 As you can see the repr of a member shows the enum name the member name and the value The str of a member shows only the enum name and member name print Weekday THURSDAY Weekday THURSDAY The type of an enumeration member is the enum it belongs to type Weekday MONDAY enum Weekday isinstance Weekday FRIDAY Weekday True Enum members have an attribute that contains just their name print Weekday TUESDAY name TUESDAY Likewise they have an attribute for their value Weekday WEDNESDAY value 3 Unlike many languages that treat enumerations solely as name value pairs Python Enums can have behavior added For example datetime date has two methods for returning the weekday weekday and isoweekday The difference is that one of them counts from 0 6 and the other from 1 7 Rather than keep track of that ourselves we can add a method to the Weekday enum to extract the day from the date instance and return the matching enum member classmethod def from_date cls date return cls date isoweekday The complete Weekday enum now looks like this class Weekday Enum MONDAY 1 TUESDAY 2 WEDNESDAY 3 THURSDAY 4 FRIDAY 5 SATURDAY 6 SUNDAY 7 classmethod def from_date cls date return cls date isoweekday Now we can find out what today is Observe from datetime import date Weekday from_date date today Weekday TUESDAY 2 Of course if you re reading this on some other day you ll see that day instead This Weekday enum is great if our variable only needs one day but what if we need several Maybe we re writing a function to plot chores during a week and don t want to use a list we could use a different type of Enum from enum import Flag class Weekday Flag MONDAY 1 TUESDAY 2 WEDNESDAY 4 THURSDAY 8 FRIDAY 16 SATURDAY 32 SUNDAY 64 We ve changed two things we re inherited from Flag and the values are all powers of 2 Just like the original Weekday enum above we can have a single selection first_week_day Weekday MONDAY first_week_day Weekday MONDAY 1 But Flag also allows us to combine several members into a single variable weekend Weekday SATURDAY Weekday SUNDAY weekend Weekday SATURDAY SUNDAY 96 You can even iterate over a Flag variable for day in weekend print day Weekday SATURDAY Weekday SUNDAY Okay let s get some chores set up chores_for_ethan feed the cat Weekday MONDAY Weekday WEDNESDAY Weekday FRIDAY do the dishes Weekday TUESDAY Weekday THURSDAY answer SO questions Weekday SATURDAY And a function to display the chores for a given day def show_chores chores day for chore days in chores items if day in days print chore show_chores chores_for_ethan Weekday SATURDAY answer SO questions In cases where the actual values of the members do not matter you can save yourself some work and use auto for the values from enum import auto class Weekday Flag MONDAY auto TUESDAY auto WEDNESDAY auto THURSDAY auto FRIDAY auto SATURDAY auto SUNDAY auto WEEKEND SATURDAY SUNDAY Programmatic access to enumeration members and their attributes Sometimes it s useful to access members in enumerations programmatically i e situations where Color RED

en

won t do because the exact color is not known at program writing time Enum allows such access Color 1 Color RED 1 Color 3 Color BLUE 3 If you want to access enum members by name use item access Color RED Color RED 1 Color GREEN Color GREEN 2 If you have an enum member and need its name or value member Color RED member name RED member value 1 Duplicating enum members and values Having two enum members with the same name is invalid class Shape Enum SQUARE 2 SQUARE 3 Traceback most recent call last TypeError SQUARE already defined as 2 However an enum member can have other names associated with it Given two entries A and B with the same value and A defined first B is an alias for the member A By value lookup of the value of A will return the member A By name lookup of A will return the member A By name lookup of B will also return the member A class Shape Enum SQUARE 2 DIAMOND 1 CIRCLE 3 ALIAS_FOR_SQUARE 2 Shape SQUARE Shape SQUARE 2 Shape ALIAS_FOR_SQUARE Shape SQUARE 2 Shape 2 Shape SQUARE 2 Note Attempting to create a member with the same name as an already defined attribute another member a method etc or attempting to create an attribute with the same name as a member is not allowed Ensuring unique enumeration values By default enumerations allow multiple names as aliases for the same value When this behavior isn t desired you can use the unique decorator from enum import Enum unique unique class Mistake Enum ONE 1 TWO 2 THREE 3 FOUR 3 Traceback most recent call last ValueError duplicate values found in enum Mistake FOUR THREE Using automatic values If the exact value is unimportant you can use auto from enum import Enum auto class Color Enum RED auto BLUE auto GREEN auto member value for member in Color 1 2 3 The values are chosen by _generate_next_value_ which can be overridden class AutoName Enum staticmethod def _generate_next_value_ name start count last_values return name class Ordinal AutoName NORTH auto SOUTH auto EAST auto WEST auto member value for member in Ordinal NORTH SOUTH EAST WEST Note The _generate_next_value_ method must be defined before any members Iteration Iterating over the members of an enum does not provide the aliases list Shape Shape SQUARE 2 Shape DIAMOND 1 Shape CIRCLE 3 list Weekday Weekday MONDAY 1 Weekday TUESDAY 2 Weekday WEDNESDAY 4 Weekday THURSDAY 8 Weekday FRIDAY 16 Weekday SATURDAY 32 Weekday SUNDAY 64 Note that the aliases Shape ALIAS_FOR_SQUARE and Weekday WEEKEND aren t shown The special attribute __members__ is a read only ordered mapping of names to members It includes all names defined in the enumeration including the aliases for name member in Shape __members__ items name member SQUARE Shape SQUARE 2 DIAMOND Shape DIAMOND 1 CIRCLE Shape CIRCLE 3 ALIAS_FOR_SQUARE Shape SQUARE 2 The __members__ attribute can be used for detailed programmatic access to the enumeration members For example finding all the aliases name for name member in Shape __members__ items if member name name ALIAS_FOR_SQUARE Note Aliases for flags include values with multiple flags set such as 3 and no flags set i e 0 Comparisons Enumeration members are compared by identity Color RED is Color RED True Color RED is Color BLUE False Color RED is not Color BLUE True Ordered comparisons between enumeration values are not supported Enum members are not integers but see IntEnum below Color RED Color BLUE Traceback most recent call last File stdin line 1 in module TypeError not supported between instances of Color and Color Equality comparisons are defined though Color BLUE Color RED False Color BLUE Color RED True Color BLUE Color BLUE True Comparisons against non enumeration values will always compare not equal again IntEnum was explicitly designed to behave differently see below Color BLUE 2 False Warning It is possible to reload modules if a reloaded module contains enums they will be recreated and the new members may not compare identical equal to the original members Allowed members and attributes of enumerations Most of the examples above use integers for enumeration values Using integers is short and handy

en

and provided by default by the Functional API but not strictly enforced In the vast majority of use cases one doesn t care what the actual value of an enumeration is But if the value is important enumerations can have arbitrary values Enumerations are Python classes and can have methods and special methods as usual If we have this enumeration class Mood Enum FUNKY 1 HAPPY 3 def describe self self is the member here return self name self value def __str__ self return my custom str 0 format self value classmethod def favorite_mood cls cls here is the enumeration return cls HAPPY Then Mood favorite_mood Mood HAPPY 3 Mood HAPPY describe HAPPY 3 str Mood FUNKY my custom str 1 The rules for what is allowed are as follows names that start and end with a single underscore are reserved by enum and cannot be used all other attributes defined within an enumeration will become members of this enumeration with the exception of special methods __str__ __add__ etc descriptors methods are also descriptors and variable names listed in _ignore_ Note if your enumeration defines __new__ and or __init__ any value s given to the enum member will be passed into those methods See Planet for an example Note The __new__ method if defined is used during creation of the Enum members it is then replaced by Enum s __new__ which is used after class creation for lookup of existing members See When to use __new__ vs __init__ for more details Restricted Enum subclassing A new Enum class must have one base enum class up to one concrete data type and as many object based mixin classes as needed The order of these base classes is class EnumName mix in data type base enum pass Also subclassing an enumeration is allowed only if the enumeration does not define any members So this is forbidden class MoreColor Color PINK 17 Traceback most recent call last TypeError enum MoreColor cannot extend enum Color But this is allowed class Foo Enum def some_behavior self pass class Bar Foo HAPPY 1 SAD 2 Allowing subclassing of enums that define members would lead to a violation of some important invariants of types and instances On the other hand it makes sense to allow sharing some common behavior between a group of enumerations See OrderedEnum for an example Dataclass support When inheriting from a dataclass the __repr__ omits the inherited class name For example from dataclasses import dataclass field dataclass class CreatureDataMixin size str legs int tail bool field repr False default True class Creature CreatureDataMixin Enum BEETLE small 6 DOG medium 4 Creature DOG Creature DOG size medium legs 4 Use the dataclass argument repr False to use the standard repr Changed in version 3 12 Only the dataclass fields are shown in the value area not the dataclass name Pickling Enumerations can be pickled and unpickled from test test_enum import Fruit from pickle import dumps loads Fruit TOMATO is loads dumps Fruit TOMATO True The usual restrictions for pickling apply picklable enums must be defined in the top level of a module since unpickling requires them to be importable from that module Note With pickle protocol version 4 it is possible to easily pickle enums nested in other classes It is possible to modify how enum members are pickled unpickled by defining __reduce_ex__ in the enumeration class The default method is by value but enums with complicated values may want to use by name import enum class MyEnum enum Enum __reduce_ex__ enum pickle_by_enum_name Note Using by name for flags is not recommended as unnamed aliases will not unpickle Functional API The Enum class is callable providing the following functional API Animal Enum Animal ANT BEE CAT DOG Animal enum Animal Animal ANT Animal ANT 1 list Animal Animal ANT 1 Animal BEE 2 Animal CAT 3 Animal DOG 4 The semantics of this API resemble namedtuple The first argument of the call to Enum is the name of the enumeration The second argument is the source of enumeration member names It can be a whitespace separated string of names a sequence of names a sequence of 2 tuples with key value pairs or a mapping e g dictionary

en

of names to values The last two options enable assigning arbitrary values to enumerations the others auto assign increasing integers starting with 1 use the start parameter to specify a different starting value A new class derived from Enum is returned In other words the above assignment to Animal is equivalent to class Animal Enum ANT 1 BEE 2 CAT 3 DOG 4 The reason for defaulting to 1 as the starting number and not 0 is that 0 is False in a boolean sense but by default enum members all evaluate to True Pickling enums created with the functional API can be tricky as frame stack implementation details are used to try and figure out which module the enumeration is being created in e g it will fail if you use a utility function in a separate module and also may not work on IronPython or Jython The solution is to specify the module name explicitly as follows Animal Enum Animal ANT BEE CAT DOG module __name__ Warning If module is not supplied and Enum cannot determine what it is the new Enum members will not be unpicklable to keep errors closer to the source pickling will be disabled The new pickle protocol 4 also in some circumstances relies on __qualname__ being set to the location where pickle will be able to find the class For example if the class was made available in class SomeData in the global scope Animal Enum Animal ANT BEE CAT DOG qualname SomeData Animal The complete signature is Enum value NewEnumName names module qualname type mixed in class start 1 value What the new enum class will record as its name names The enum members This can be a whitespace or comma separated string values will start at 1 unless otherwise specified RED GREEN BLUE RED GREEN BLUE RED GREEN BLUE or an iterator of names RED GREEN BLUE or an iterator of name value pairs CYAN 4 MAGENTA 5 YELLOW 6 or a mapping CHARTREUSE 7 SEA_GREEN 11 ROSEMARY 42 module name of module where new enum class can be found qualname where in module new enum class can be found type type to mix in to new enum class start number to start counting at if only names are passed in Changed in version 3 5 The start parameter was added Derived Enumerations IntEnum The first variation of Enum that is provided is also a subclass of int Members of an IntEnum can be compared to integers by extension integer enumerations of different types can also be compared to each other from enum import IntEnum class Shape IntEnum CIRCLE 1 SQUARE 2 class Request IntEnum POST 1 GET 2 Shape 1 False Shape CIRCLE 1 True Shape CIRCLE Request POST True However they still can t be compared to standard Enum enumerations class Shape IntEnum CIRCLE 1 SQUARE 2 class Color Enum RED 1 GREEN 2 Shape CIRCLE Color RED False IntEnum values behave like integers in other ways you d expect int Shape CIRCLE 1 a b c Shape CIRCLE b i for i in range Shape SQUARE 0 1 StrEnum The second variation of Enum that is provided is also a subclass of str Members of a StrEnum can be compared to strings by extension string enumerations of different types can also be compared to each other New in version 3 11 IntFlag The next variation of Enum provided IntFlag is also based on int The difference being IntFlag members can be combined using the bitwise operators and the result is still an IntFlag member if possible Like IntEnum IntFlag members are also integers and can be used wherever an int is used Note Any operation on an IntFlag member besides the bit wise operations will lose the IntFlag membership Bit wise operations that result in invalid IntFlag values will lose the IntFlag membership See FlagBoundary for details New in version 3 6 Changed in version 3 11 Sample IntFlag class from enum import IntFlag class Perm IntFlag R 4 W 2 X 1 Perm R Perm W Perm R W 6 Perm R Perm W 6 RW Perm R Perm W Perm R in RW True It is also possible to name the combinations class Perm IntFlag R 4 W 2 X 1 RWX 7 Perm RWX Perm RWX 7 Perm RWX Perm 0 Perm 7 Perm RWX 7 Note Named combinations are considered aliases Aliases do not show up during iteration but can be returned from by value lookups Changed in version 3 11 Another important difference betwe

en

en IntFlag and Enum is that if no flags are set the value is 0 its boolean evaluation is False Perm R Perm X Perm 0 bool Perm R Perm X False Because IntFlag members are also subclasses of int they can be combined with them but may lose IntFlag membership Perm X 4 Perm R X 5 Perm X 8 9 Note The negation operator always returns an IntFlag member with a positive value Perm X value Perm R Perm W value 6 True IntFlag members can also be iterated over list RW Perm R 4 Perm W 2 New in version 3 11 Flag The last variation is Flag Like IntFlag Flag members can be combined using the bitwise operators Unlike IntFlag they cannot be combined with nor compared against any other Flag enumeration nor int While it is possible to specify the values directly it is recommended to use auto as the value and let Flag select an appropriate value New in version 3 6 Like IntFlag if a combination of Flag members results in no flags being set the boolean evaluation is False from enum import Flag auto class Color Flag RED auto BLUE auto GREEN auto Color RED Color GREEN Color 0 bool Color RED Color GREEN False Individual flags should have values that are powers of two 1 2 4 8 while combinations of flags will not class Color Flag RED auto BLUE auto GREEN auto WHITE RED BLUE GREEN Color WHITE Color WHITE 7 Giving a name to the no flags set condition does not change its boolean value class Color Flag BLACK 0 RED auto BLUE auto GREEN auto Color BLACK Color BLACK 0 bool Color BLACK False Flag members can also be iterated over purple Color RED Color BLUE list purple Color RED 1 Color BLUE 2 New in version 3 11 Note For the majority of new code Enum and Flag are strongly recommended since IntEnum and IntFlag break some semantic promises of an enumeration by being comparable to integers and thus by transitivity to other unrelated enumerations IntEnum and IntFlag should be used only in cases where Enum and Flag will not do for example when integer constants are replaced with enumerations or for interoperability with other systems Others While IntEnum is part of the enum module it would be very simple to implement independently class IntEnum int Enum pass This demonstrates how similar derived enumerations can be defined for example a FloatEnum that mixes in float instead of int Some rules 1 When subclassing Enum mix in types must appear before Enum itself in the sequence of bases as in the IntEnum example above 2 Mix in types must be subclassable For example bool and range are not subclassable and will throw an error during Enum creation if used as the mix in type 3 While Enum can have members of any type once you mix in an additional type all the members must have values of that type e g int above This restriction does not apply to mix ins which only add methods and don t specify another type 4 When another data type is mixed in the value attribute is not the same as the enum member itself although it is equivalent and will compare equal 5 A data type is a mixin that defines __new__ or a dataclass 6 style formatting s and r call the Enum class s __str__ and __repr__ respectively other codes such as i or h for IntEnum treat the enum member as its mixed in type 7 Formatted string literals str format and format will use the enum s __str__ method Note Because IntEnum IntFlag and StrEnum are designed to be drop in replacements for existing constants their __str__ method has been reset to their data types __str__ method When to use __new__ vs __init__ __new__ must be used whenever you want to customize the actual value of the Enum member Any other modifications may go in either __new__ or __init__ with __init__ being preferred For example if you want to pass several items to the constructor but only want one of them to be the value class Coordinate bytes Enum Coordinate with binary codes that can be indexed by the int code def __new__ cls value label unit obj bytes __new__ cls value obj _value_ value obj label label obj unit unit return obj PX 0 P X km PY 1 P Y km VX 2 V X km s VY 3 V Y km s print Coordinate PY Coordinate PY print Coordinate 3 Coordinate VY Warning

en

Do not call super __new__ as the lookup only __new__ is the one that is found instead use the data type directly Finer Points Supported __dunder__ names __members__ is a read only ordered mapping of member_name member items It is only available on the class __new__ if specified must create and return the enum members it is also a very good idea to set the member s _value_ appropriately Once all the members are created it is no longer used Supported _sunder_ names _name_ name of the member _value_ value of the member can be set modified in __new__ _missing_ a lookup function used when a value is not found may be overridden _ignore_ a list of names either as a list or a str that will not be transformed into members and will be removed from the final class _order_ used in Python 2 3 code to ensure member order is consistent class attribute removed during class creation _generate_next_value_ used by the Functional API and by auto to get an appropriate value for an enum member may be overridden Note For standard Enum classes the next value chosen is the last value seen incremented by one For Flag classes the next value chosen will be the next highest power of two regardless of the last value seen New in version 3 6 _missing_ _order_ _generate_next_value_ New in version 3 7 _ignore_ To help keep Python 2 Python 3 code in sync an _order_ attribute can be provided It will be checked against the actual order of the enumeration and raise an error if the two do not match class Color Enum _order_ RED GREEN BLUE RED 1 BLUE 3 GREEN 2 Traceback most recent call last TypeError member order does not match _order_ RED BLUE GREEN RED GREEN BLUE Note In Python 2 code the _order_ attribute is necessary as definition order is lost before it can be recorded _Private__names Private names are not converted to enum members but remain normal attributes Changed in version 3 11 Enum member type Enum members are instances of their enum class and are normally accessed as EnumClass member In certain situations such as writing custom enum behavior being able to access one member directly from another is useful and is supported however in order to avoid name clashes between member names and attributes methods from mixed in classes upper case names are strongly recommended Changed in version 3 5 Creating members that are mixed with other data types When subclassing other data types such as int or str with an Enum all values after the are passed to that data type s constructor For example class MyEnum IntEnum help int int x base 10 integer example 11 16 so x 11 and base 16 MyEnum example value and hex 11 is 17 Boolean value of Enum classes and members Enum classes that are mixed with non Enum types such as int str etc are evaluated according to the mixed in type s rules otherwise all members evaluate as True To make your own enum s boolean evaluation depend on the member s value add the following to your class def __bool__ self return bool self value Plain Enum classes always evaluate as True Enum classes with methods If you give your enum subclass extra methods like the Planet class below those methods will show up in a dir of the member but not of the class dir Planet EARTH JUPITER MARS MERCURY NEPTUNE SATURN URANUS VENUS __class__ __doc__ __members__ __module__ dir Planet EARTH __class__ __doc__ __module__ mass name radius surface_gravity value Combining members of Flag Iterating over a combination of Flag members will only return the members that are comprised of a single bit class Color Flag RED auto GREEN auto BLUE auto MAGENTA RED BLUE YELLOW RED GREEN CYAN GREEN BLUE Color 3 named combination Color YELLOW 3 Color 7 not named combination Color RED GREEN BLUE 7 Flag and IntFlag minutia Using the following snippet for our examples class Color IntFlag BLACK 0 RED 1 GREEN 2 BLUE 4 PURPLE RED BLUE WHITE RED GREEN BLUE the following are true single bit flags are canonical multi bit and zero bit flags are aliases only canonical flags are returned during iteration list Color WHITE Color RED 1 Color GREEN 2 Color BLUE 4 negating a flag or flag set returns a

en

new flag flag set with the corresponding positive integer value Color BLUE Color BLUE 4 Color BLUE Color RED GREEN 3 names of pseudo flags are constructed from their members names Color RED Color GREEN name RED GREEN multi bit flags aka aliases can be returned from operations Color RED Color BLUE Color PURPLE 5 Color 7 or Color 1 Color WHITE 7 Color 0 Color BLACK 0 membership containment checking zero valued flags are always considered to be contained Color BLACK in Color WHITE True otherwise only if all bits of one flag are in the other flag will True be returned Color PURPLE in Color WHITE True Color GREEN in Color PURPLE False There is a new boundary mechanism that controls how out of range invalid bits are handled STRICT CONFORM EJECT and KEEP STRICT raises an exception when presented with invalid values CONFORM discards any invalid bits EJECT lose Flag status and become a normal int with the given value KEEP keep the extra bits keeps Flag status and extra bits extra bits do not show up in iteration extra bits do show up in repr and str The default for Flag is STRICT the default for IntFlag is EJECT and the default for _convert_ is KEEP see ssl Options for an example of when KEEP is needed How are Enums and Flags different Enums have a custom metaclass that affects many aspects of both derived Enum classes and their instances members Enum Classes The EnumType metaclass is responsible for providing the __contains__ __dir__ __iter__ and other methods that allow one to do things with an Enum class that fail on a typical class such as list Color or some_enum_var in Color EnumType is responsible for ensuring that various other methods on the final Enum class are correct such as __new__ __getnewargs__ __str__ and __repr__ Flag Classes Flags have an expanded view of aliasing to be canonical the value of a flag needs to be a power of two value and not a duplicate name So in addition to the Enum definition of alias a flag with no value a k a 0 or with more than one power of two value e g 3 is considered an alias Enum Members aka instances The most interesting thing about enum members is that they are singletons EnumType creates them all while it is creating the enum class itself and then puts a custom __new__ in place to ensure that no new ones are ever instantiated by returning only the existing member instances Flag Members Flag members can be iterated over just like the Flag class and only the canonical members will be returned For example list Color Color RED 1 Color GREEN 2 Color BLUE 4 Note that BLACK PURPLE and WHITE do not show up Inverting a flag member returns the corresponding positive value rather than a negative value for example Color RED Color GREEN BLUE 6 Flag members have a length corresponding to the number of power of two values they contain For example len Color PURPLE 2 Enum Cookbook While Enum IntEnum StrEnum Flag and IntFlag are expected to cover the majority of use cases they cannot cover them all Here are recipes for some different types of enumerations that can be used directly or as examples for creating one s own Omitting values In many use cases one doesn t care what the actual value of an enumeration is There are several ways to define this type of simple enumeration use instances of auto for the value use instances of object as the value use a descriptive string as the value use a tuple as the value and a custom __new__ to replace the tuple with an int value Using any of these methods signifies to the user that these values are not important and also enables one to add remove or reorder members without having to renumber the remaining members Using auto Using auto would look like class Color Enum RED auto BLUE auto GREEN auto Color GREEN Color GREEN 3 Using object Using object would look like class Color Enum RED object GREEN object BLUE object Color GREEN Color GREEN object object at 0x This is also a good example of why you might want to write your own __repr__ class Color Enum RED object GREEN object BLUE object def __repr__ self return s s self __class__ __name__ self _name_ Color GREEN Col

en

or GREEN Using a descriptive string Using a string as the value would look like class Color Enum RED stop GREEN go BLUE too fast Color GREEN Color GREEN go Using a custom __new__ Using an auto numbering __new__ would look like class AutoNumber Enum def __new__ cls value len cls __members__ 1 obj object __new__ cls obj _value_ value return obj class Color AutoNumber RED GREEN BLUE Color GREEN Color GREEN 2 To make a more general purpose AutoNumber add args to the signature class AutoNumber Enum def __new__ cls args this is the only change from above value len cls __members__ 1 obj object __new__ cls obj _value_ value return obj Then when you inherit from AutoNumber you can write your own __init__ to handle any extra arguments class Swatch AutoNumber def __init__ self pantone unknown self pantone pantone AUBURN 3497 SEA_GREEN 1246 BLEACHED_CORAL New color no Pantone code yet Swatch SEA_GREEN Swatch SEA_GREEN 2 Swatch SEA_GREEN pantone 1246 Swatch BLEACHED_CORAL pantone unknown Note The __new__ method if defined is used during creation of the Enum members it is then replaced by Enum s __new__ which is used after class creation for lookup of existing members Warning Do not call super __new__ as the lookup only __new__ is the one that is found instead use the data type directly e g obj int __new__ cls value OrderedEnum An ordered enumeration that is not based on IntEnum and so maintains the normal Enum invariants such as not being comparable to other enumerations class OrderedEnum Enum def __ge__ self other if self __class__ is other __class__ return self value other value return NotImplemented def __gt__ self other if self __class__ is other __class__ return self value other value return NotImplemented def __le__ self other if self __class__ is other __class__ return self value other value return NotImplemented def __lt__ self other if self __class__ is other __class__ return self value other value return NotImplemented class Grade OrderedEnum A 5 B 4 C 3 D 2 F 1 Grade C Grade A True DuplicateFreeEnum Raises an error if a duplicate member value is found instead of creating an alias class DuplicateFreeEnum Enum def __init__ self args cls self __class__ if any self value e value for e in cls a self name e cls self value name raise ValueError aliases not allowed in DuplicateFreeEnum r r a e class Color DuplicateFreeEnum RED 1 GREEN 2 BLUE 3 GRENE 2 Traceback most recent call last ValueError aliases not allowed in DuplicateFreeEnum GRENE GREEN Note This is a useful example for subclassing Enum to add or change other behaviors as well as disallowing aliases If the only desired change is disallowing aliases the unique decorator can be used instead Planet If __new__ or __init__ is defined the value of the enum member will be passed to those methods class Planet Enum MERCURY 3 303e 23 2 4397e6 VENUS 4 869e 24 6 0518e6 EARTH 5 976e 24 6 37814e6 MARS 6 421e 23 3 3972e6 JUPITER 1 9e 27 7 1492e7 SATURN 5 688e 26 6 0268e7 URANUS 8 686e 25 2 5559e7 NEPTUNE 1 024e 26 2 4746e7 def __init__ self mass radius self mass mass in kilograms self radius radius in meters property def surface_gravity self universal gravitational constant m3 kg 1 s 2 G 6 67300E 11 return G self mass self radius self radius Planet EARTH value 5 976e 24 6378140 0 Planet EARTH surface_gravity 9 802652743337129 TimePeriod An example to show the _ignore_ attribute in use from datetime import timedelta class Period timedelta Enum different lengths of time _ignore_ Period i Period vars for i in range 367 Period day_ d i i list Period 2 Period day_0 datetime timedelta 0 Period day_1 datetime timedelta days 1 list Period 2 Period day_365 datetime timedelta days 365 Period day_366 datetime timedelta days 366 Subclassing EnumType While most enum needs can be met by customizing Enum subclasses either with class decorators or custom functions EnumType can be subclassed to provide a different Enum experience

en

Exceptions Source code Lib asyncio exceptions py exception asyncio TimeoutError A deprecated alias of TimeoutError raised when the operation has exceeded the given deadline Changed in version 3 11 This class was made an alias of TimeoutError exception asyncio CancelledError The operation has been cancelled This exception can be caught to perform custom operations when asyncio Tasks are cancelled In almost all situations the exception must be re raised Changed in version 3 8 CancelledError is now a subclass of BaseException rather than Exception exception asyncio InvalidStateError Invalid internal state of Task or Future Can be raised in situations like setting a result value for a Future object that already has a result value set exception asyncio SendfileNotAvailableError The sendfile syscall is not available for the given socket or file type A subclass of RuntimeError exception asyncio IncompleteReadError The requested read operation did not complete fully Raised by the asyncio stream APIs This exception is a subclass of EOFError expected The total number int of expected bytes partial A string of bytes read before the end of stream was reached exception asyncio LimitOverrunError Reached the buffer size limit while looking for a separator Raised by the asyncio stream APIs consumed The total number of to be consumed bytes

en

Set Objects This section details the public API for set and frozenset objects Any functionality not listed below is best accessed using either the abstract object protocol including PyObject_CallMethod PyObject_RichCompareBool PyObject_Hash PyObject_Repr PyObject_IsTrue PyObject_Print and PyObject_GetIter or the abstract number protocol including PyNumber_And PyNumber_Subtract PyNumber_Or PyNumber_Xor PyNumber_InPlaceAnd PyNumber_InPlaceSubtract PyNumber_InPlaceOr and PyNumber_InPlaceXor type PySetObject This subtype of PyObject is used to hold the internal data for both set and frozenset objects It is like a PyDictObject in that it is a fixed size for small sets much like tuple storage and will point to a separate variable sized block of memory for medium and large sized sets much like list storage None of the fields of this structure should be considered public and all are subject to change All access should be done through the documented API rather than by manipulating the values in the structure PyTypeObject PySet_Type Part of the Stable ABI This is an instance of PyTypeObject representing the Python set type PyTypeObject PyFrozenSet_Type Part of the Stable ABI This is an instance of PyTypeObject representing the Python frozenset type The following type check macros work on pointers to any Python object Likewise the constructor functions work with any iterable Python object int PySet_Check PyObject p Return true if p is a set object or an instance of a subtype This function always succeeds int PyFrozenSet_Check PyObject p Return true if p is a frozenset object or an instance of a subtype This function always succeeds int PyAnySet_Check PyObject p Return true if p is a set object a frozenset object or an instance of a subtype This function always succeeds int PySet_CheckExact PyObject p Return true if p is a set object but not an instance of a subtype This function always succeeds New in version 3 10 int PyAnySet_CheckExact PyObject p Return true if p is a set object or a frozenset object but not an instance of a subtype This function always succeeds int PyFrozenSet_CheckExact PyObject p Return true if p is a frozenset object but not an instance of a subtype This function always succeeds PyObject PySet_New PyObject iterable Return value New reference Part of the Stable ABI Return a new set containing objects returned by the iterable The iterable may be NULL to create a new empty set Return the new set on success or NULL on failure Raise TypeError if iterable is not actually iterable The constructor is also useful for copying a set c set s PyObject PyFrozenSet_New PyObject iterable Return value New reference Part of the Stable ABI Return a new frozenset containing objects returned by the iterable The iterable may be NULL to create a new empty frozenset Return the new set on success or NULL on failure Raise TypeError if iterable is not actually iterable The following functions and macros are available for instances of set or frozenset or instances of their subtypes Py_ssize_t PySet_Size PyObject anyset Part of the Stable ABI Return the length of a set or frozenset object Equivalent to len anyset Raises a SystemError if anyset is not a set frozenset or an instance of a subtype Py_ssize_t PySet_GET_SIZE PyObject anyset Macro form of PySet_Size without error checking int PySet_Contains PyObject anyset PyObject key Part of the Stable ABI Return 1 if found 0 if not found and 1 if an error is encountered Unlike the Python __contains__ method this function does not automatically convert unhashable sets into temporary frozensets Raise a TypeError if the key is unhashable Raise SystemError if anyset is not a set frozenset or an instance of a subtype int PySet_Add PyObject set PyObject key Part of the Stable ABI Add key to a set instance Also works with frozenset instances like PyTuple_SetItem it can be used to fill in the values of brand new frozensets before they are exposed to other code Return 0 on success or 1 on failure Raise a TypeError if the key is unhashable Raise a MemoryError if there is no room to grow Raise a System

en

Error if set is not an instance of set or its subtype The following functions are available for instances of set or its subtypes but not for instances of frozenset or its subtypes int PySet_Discard PyObject set PyObject key Part of the Stable ABI Return 1 if found and removed 0 if not found no action taken and 1 if an error is encountered Does not raise KeyError for missing keys Raise a TypeError if the key is unhashable Unlike the Python discard method this function does not automatically convert unhashable sets into temporary frozensets Raise SystemError if set is not an instance of set or its subtype PyObject PySet_Pop PyObject set Return value New reference Part of the Stable ABI Return a new reference to an arbitrary object in the set and removes the object from the set Return NULL on failure Raise KeyError if the set is empty Raise a SystemError if set is not an instance of set or its subtype int PySet_Clear PyObject set Part of the Stable ABI Empty an existing set of all elements Return 0 on success Return 1 and raise SystemError if set is not an instance of set or its subtype

en