Python 3.9 的新功能 ¶

字典合并 & 更新运算符 ¶

合并 ( | ) 和更新 ( |= ) operators have been added to the built-in dict class. Those complement the existing dict.update and {**d1, **d2} methods of merging dictionaries.

范例：

>>> x = {"key1": "value1 from x", "key2": "value2 from x"}
>>> y = {"key2": "value2 from y", "key3": "value3 from y"}
>>> x | y
{'key1': 'value1 from x', 'key2': 'value2 from y', 'key3': 'value3 from y'}
>>> y | x
{'key2': 'value2 from x', 'key3': 'value3 from y', 'key1': 'value1 from x'}
									

见 PEP 584 for a full description. (Contributed by Brandt Bucher in bpo-36144 .)

移除前缀和后缀的新字符串方法 ¶

str.removeprefix(prefix) and str.removesuffix(suffix) have been added to easily remove an unneeded prefix or a suffix from a string. Corresponding bytes , bytearray ，和 collections.UserString methods have also been added. See PEP 616 for a full description. (Contributed by Dennis Sweeney in bpo-39939 .)

标准集合中的类型提示泛型 ¶

In type annotations you can now use built-in collection types such as list and dict as generic types instead of importing the corresponding capitalized types (e.g. List or Dict ) from typing . Some other types in the standard library are also now generic, for example queue.Queue .

范例：

def greet_all(names: list[str]) -> None:
    for name in names:
        print("Hello", name)
									

见 PEP 585 for more details. (Contributed by Guido van Rossum, Ethan Smith, and Batuhan Taşkaya in bpo-39481 .)

新的剖析器 ¶

Python 3.9 uses a new parser, based on PEG 而不是 LL(1) . The new parser’s performance is roughly comparable to that of the old parser, but the PEG formalism is more flexible than LL(1) when it comes to designing new language features. We’ll start using this flexibility in Python 3.10 and later.

ast module uses the new parser and produces the same AST as the old parser.

In Python 3.10, the old parser will be deleted and so will all functionality that depends on it (primarily the parser module, which has long been deprecated). In Python 3.9 only , you can switch back to the LL(1) parser using a command line switch ( -X oldparser ) or an environment variable ( PYTHONOLDPARSER=1 ).

见 PEP 617 for more details. (Contributed by Guido van Rossum, Pablo Galindo and Lysandros Nikolaou in bpo-40334 .)

zoneinfo ¶

zoneinfo module brings support for the IANA time zone database to the standard library. It adds zoneinfo.ZoneInfo , a concrete datetime.tzinfo implementation backed by the system’s time zone data.

范例：

>>> from zoneinfo import ZoneInfo
>>> from datetime import datetime, timedelta
>>> # Daylight saving time
>>> dt = datetime(2020, 10, 31, 12, tzinfo=ZoneInfo("America/Los_Angeles"))
>>> print(dt)
2020-10-31 12:00:00-07:00
>>> dt.tzname()
'PDT'
>>> # Standard time
>>> dt += timedelta(days=7)
>>> print(dt)
2020-11-07 12:00:00-08:00
>>> print(dt.tzname())
PST
									

As a fall-back source of data for platforms that don’t ship the IANA database, the tzdata module was released as a first-party package – distributed via PyPI and maintained by the CPython core team.

graphlib ¶

新的模块， graphlib , was added that contains the graphlib.TopologicalSorter class to offer functionality to perform topological sorting of graphs. (Contributed by Pablo Galindo, Tim Peters and Larry Hastings in bpo-17005 .)

ast ¶

添加 indent 选项到 dump() which allows it to produce a multiline indented output. (Contributed by Serhiy Storchaka in bpo-37995 .)

添加 ast.unparse() as a function in the ast module that can be used to unparse an ast.AST object and produce a string with code that would produce an equivalent ast.AST object when parsed. (Contributed by Pablo Galindo and Batuhan Taskaya in bpo-38870 .)

Added docstrings to AST nodes that contains the ASDL signature used to construct that node. (Contributed by Batuhan Taskaya in bpo-39638 .)

asyncio ¶

Due to significant security concerns, the reuse_address parameter of asyncio.loop.create_datagram_endpoint() is no longer supported. This is because of the behavior of the socket option SO_REUSEADDR in UDP. For more details, see the documentation for loop.create_datagram_endpoint() . (Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in bpo-37228 .)

添加新 协程 shutdown_default_executor() that schedules a shutdown for the default executor that waits on the ThreadPoolExecutor to finish closing. Also, asyncio.run() has been updated to use the new 协程 . (Contributed by Kyle Stanley in bpo-34037 .)

添加 asyncio.PidfdChildWatcher , a Linux-specific child watcher implementation that polls process file descriptors. ( bpo-38692 )

添加新 协程 asyncio.to_thread() . It is mainly used for running IO-bound functions in a separate thread to avoid blocking the event loop, and essentially works as a high-level version of run_in_executor() that can directly take keyword arguments. (Contributed by Kyle Stanley and Yury Selivanov in bpo-32309 .)

When cancelling the task due to a timeout, asyncio.wait_for() will now wait until the cancellation is complete also in the case when timeout is <= 0, like it does with positive timeouts. (Contributed by Elvis Pranskevichus in bpo-32751 .)

asyncio 现在引发 TyperError when calling incompatible methods with an ssl.SSLSocket socket. (Contributed by Ido Michael in bpo-37404 .)

compileall ¶

Added new possibility to use hardlinks for duplicated .pyc 文件： hardlink_dupes parameter and –hardlink-dupes command line option. (Contributed by Lumír ‘Frenzy’ Balhar in bpo-40495 .)

Added new options for path manipulation in resulting .pyc 文件： stripdir , prependdir , limit_sl_dest parameters and -s, -p, -e command line options. Added the possibility to specify the option for an optimization level multiple times. (Contributed by Lumír ‘Frenzy’ Balhar in bpo-38112 .)

concurrent.futures ¶

添加新 cancel_futures 参数到 concurrent.futures.Executor.shutdown() that cancels all pending futures which have not started running, instead of waiting for them to complete before shutting down the executor. (Contributed by Kyle Stanley in bpo-39349 .)

Removed daemon threads from ThreadPoolExecutor and ProcessPoolExecutor . This improves compatibility with subinterpreters and predictability in their shutdown processes. (Contributed by Kyle Stanley in bpo-39812 .)

Workers in ProcessPoolExecutor are now spawned on demand, only when there are no available idle workers to reuse. This optimizes startup overhead and reduces the amount of lost CPU time to idle workers. (Contributed by Kyle Stanley in bpo-39207 .)

curses ¶

添加 curses.get_escdelay() , curses.set_escdelay() , curses.get_tabsize() ，和 curses.set_tabsize() functions. (Contributed by Anthony Sottile in bpo-38312 .)

datetime ¶

isocalendar() of datetime.date and isocalendar() of datetime.datetime 方法现在返回 namedtuple() 而不是 tuple 。(贡献由 Dong-hee Na 在 bpo-24416 .)

distutils ¶

upload command now creates SHA2-256 and Blake2b-256 hash digests. It skips MD5 on platforms that block MD5 digest. (Contributed by Christian Heimes in bpo-40698 .)

fcntl ¶

添加常量 F_OFD_GETLK , F_OFD_SETLK and F_OFD_SETLKW 。(贡献由 Dong-hee Na 在 bpo-38602 .)

ftplib ¶

FTP and FTP_TLS 现在引发 ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. (Contributed by Dong-hee Na in bpo-39259 .)

gc ¶

When the garbage collector makes a collection in which some objects resurrect (they are reachable from outside the isolated cycles after the finalizers have been executed), do not block the collection of all objects that are still unreachable. (Contributed by Pablo Galindo and Tim Peters in bpo-38379 .)

添加新函数 gc.is_finalized() to check if an object has been finalized by the garbage collector. (Contributed by Pablo Galindo in bpo-39322 .)

hashlib ¶

hashlib module can now use SHA3 hashes and SHAKE XOF from OpenSSL when available. (Contributed by Christian Heimes in bpo-37630 .)

Builtin hash modules can now be disabled with ./configure --without-builtin-hashlib-hashes or selectively enabled with e.g. ./configure --with-builtin-hashlib-hashes=sha3,blake2 to force use of OpenSSL based implementation. (Contributed by Christian Heimes in bpo-40479 )

http ¶

HTTP 状态码 103 EARLY_HINTS , 418 IM_A_TEAPOT and 425 TOO_EARLY 被添加到 http.HTTPStatus 。(贡献由 Dong-hee Na 在 bpo-39509 and Ross Rhodes in bpo-39507 .)

IDLE and idlelib ¶

Added option to toggle cursor blink off. (Contributed by Zackery Spytz in bpo-4603 .)

Escape key now closes IDLE completion windows. (Contributed by Johnny Najera in bpo-38944 .)

Added keywords to module name completion list. (Contributed by Terry J. Reedy in bpo-37765 .)

The changes above have been backported to 3.8 maintenance releases.

imaplib ¶

IMAP4 and IMAP4_SSL now have an optional timeout parameter for their constructors. Also, the open() method now has an optional timeout parameter with this change. The overridden methods of IMAP4_SSL and IMAP4_stream were applied to this change. (Contributed by Dong-hee Na in bpo-38615 .)

imaplib.IMAP4.unselect() is added. imaplib.IMAP4.unselect() frees server’s resources associated with the selected mailbox and returns the server to the authenticated state. This command performs the same actions as imaplib.IMAP4.close() , except that no messages are permanently removed from the currently selected mailbox. (Contributed by Dong-hee Na in bpo-40375 .)

importlib ¶

To improve consistency with import statements, importlib.util.resolve_name() 现在引发 ImportError 而不是 ValueError for invalid relative import attempts. (Contributed by Ngalim Siregar in bpo-37444 .)

Import loaders which publish immutable module objects can now publish immutable packages in addition to individual modules. (Contributed by Dino Viehland in bpo-39336 .)

添加 importlib.resources.files() function with support for subdirectories in package data, matching backport in importlib_resources version 1.5. (Contributed by Jason R. Coombs in bpo-39791 .)

Refreshed importlib.metadata from importlib_metadata version 1.6.1.

inspect ¶

inspect.BoundArguments.arguments is changed from OrderedDict to regular dict. (Contributed by Inada Naoki in bpo-36350 and bpo-39775 .)

ipaddress ¶

ipaddress now supports IPv6 Scoped Addresses (IPv6 address with suffix %<scope_id> ).

Scoped IPv6 addresses can be parsed using ipaddress.IPv6Address . If present, scope zone ID is available through the scope_id attribute. (Contributed by Oleksandr Pavliuk in bpo-34788 .)

Starting with Python 3.9.5 the ipaddress module no longer accepts any leading zeros in IPv4 address strings. (Contributed by Christian Heimes in bpo-36384 ).

math ¶

Expanded the math.gcd() function to handle multiple arguments. Formerly, it only supported two arguments. (Contributed by Serhiy Storchaka in bpo-39648 .)

添加 math.lcm() : return the least common multiple of specified arguments. (Contributed by Mark Dickinson, Ananthakrishnan and Serhiy Storchaka in bpo-39479 and bpo-39648 .)

添加 math.nextafter() : return the next floating-point value after x towards y . (Contributed by Victor Stinner in bpo-39288 .)

添加 math.ulp() : return the value of the least significant bit of a float. (Contributed by Victor Stinner in bpo-39310 .)

multiprocessing ¶

multiprocessing.SimpleQueue class has a new close() method to explicitly close the queue. (Contributed by Victor Stinner in bpo-30966 .)

nntplib ¶

NNTP and NNTP_SSL 现在引发 ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. (Contributed by Dong-hee Na in bpo-39259 .)

os ¶

添加 CLD_KILLED and CLD_STOPPED for si_code 。(贡献由 Dong-hee Na 在 bpo-38493 .)

Exposed the Linux-specific os.pidfd_open() ( bpo-38692 ) 和 os.P_PIDFD ( bpo-38713 ) for process management with file descriptors.

os.unsetenv() function is now also available on Windows. (Contributed by Victor Stinner in bpo-39413 .)

os.putenv() and os.unsetenv() functions are now always available. (Contributed by Victor Stinner in bpo-39395 .)

添加 os.waitstatus_to_exitcode() function: convert a wait status to an exit code. (Contributed by Victor Stinner in bpo-40094 .)

pathlib ¶

添加 pathlib.Path.readlink() which acts similarly to os.readlink() . (Contributed by Girts Folkmanis in bpo-30618 )

pdb ¶

On Windows now Pdb supports ~/.pdbrc . (Contributed by Tim Hopper and Dan Lidral-Porter in bpo-20523 .)

poplib ¶

POP3 and POP3_SSL 现在引发 ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. (Contributed by Dong-hee Na in bpo-39259 .)

pprint ¶

pprint can now pretty-print types.SimpleNamespace . (Contributed by Carl Bordum Hansen in bpo-37376 .)

pydoc ¶

The documentation string is now shown not only for class, function, method etc, but for any object that has its own __doc__ attribute. (Contributed by Serhiy Storchaka in bpo-40257 .)

random ¶

添加新 random.Random.randbytes method: generate random bytes. (Contributed by Victor Stinner in bpo-40286 .)

signal ¶

Exposed the Linux-specific signal.pidfd_send_signal() for sending to signals to a process using a file descriptor instead of a pid. ( bpo-38712 )

smtplib ¶

SMTP and SMTP_SSL 现在引发 ValueError if the given timeout for their constructor is zero to prevent the creation of a non-blocking socket. (Contributed by Dong-hee Na in bpo-39259 .)

LMTP constructor now has an optional timeout parameter. (Contributed by Dong-hee Na in bpo-39329 .)

socket ¶

socket module now exports the CAN_RAW_JOIN_FILTERS constant on Linux 4.1 and greater. (Contributed by Stefan Tatschner and Zackery Spytz in bpo-25780 .)

The socket module now supports the CAN_J1939 protocol on platforms that support it. (Contributed by Karl Ding in bpo-40291 .)

The socket module now has the socket.send_fds() and socket.recv_fds() functions. (Contributed by Joannah Nanjekye, Shinya Okano and Victor Stinner in bpo-28724 .)

time ¶

On AIX, thread_time() is now implemented with thread_cputime() which has nanosecond resolution, rather than clock_gettime(CLOCK_THREAD_CPUTIME_ID) which has a resolution of 10 ms. (Contributed by Batuhan Taskaya in bpo-40192 )

sys ¶

添加新 sys.platlibdir attribute: name of the platform-specific library directory. It is used to build the path of standard library and the paths of installed extension modules. It is equal to "lib" on most platforms. On Fedora and SuSE, it is equal to "lib64" on 64-bit platforms. (Contributed by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor Stinner in bpo-1294959 .)

先前， sys.stderr was block-buffered when non-interactive. Now stderr defaults to always being line-buffered. (Contributed by Jendrik Seipp in bpo-13601 .)

tracemalloc ¶

添加 tracemalloc.reset_peak() to set the peak size of traced memory blocks to the current size, to measure the peak of specific pieces of code. (Contributed by Huon Wilson in bpo-40630 .)

typing ¶

PEP 593 introduced an typing.Annotated type to decorate existing types with context-specific metadata and new include_extras 参数到 typing.get_type_hints() to access the metadata at runtime. (Contributed by Till Varoquaux and Konstantin Kashin.)

unicodedata ¶

The Unicode database has been updated to version 13.0.0. ( bpo-39926 ).

venv ¶

The activation scripts provided by venv now all specify their prompt customization consistently by always using the value specified by __VENV_PROMPT__ . Previously some scripts unconditionally used __VENV_PROMPT__ , others only if it happened to be set (which was the default case), and one used __VENV_NAME__ instead. (Contributed by Brett Cannon in bpo-37663 .)

xml ¶

White space characters within attributes are now preserved when serializing xml.etree.ElementTree to XML file. EOLNs are no longer normalized to “n”. This is the result of discussion about how to interpret section 2.11 of XML spec. (Contributed by Mefistotelis in bpo-39011 .)

Python API 变化 ¶

• __import__() and importlib.util.resolve_name() 现在引发 ImportError where it previously raised ValueError . Callers catching the specific exception type and supporting both Python 3.9 and earlier versions will need to catch both using except (ImportError, ValueError): .

• venv activation scripts no longer special-case when __VENV_PROMPT__ 被设为 "" .

• select.epoll.unregister() method no longer ignores the EBADF error. (Contributed by Victor Stinner in bpo-39239 .)

• compresslevel parameter of bz2.BZ2File became keyword-only, since the buffering parameter has been removed. (Contributed by Victor Stinner in bpo-39357 .)

• Simplified AST for subscription. Simple indices will be represented by their value, extended slices will be represented as tuples. Index(value) will return a value itself, ExtSlice(slices) 将返回 Tuple(slices, Load()) . (Contributed by Serhiy Storchaka in bpo-34822 .)

• importlib module now ignores the PYTHONCASEOK environment variable when the -E or -I command line options are being used.

• encoding parameter has been added to the classes ftplib.FTP and ftplib.FTP_TLS as a keyword-only parameter, and the default encoding is changed from Latin-1 to UTF-8 to follow RFC 2640 .

• asyncio.loop.shutdown_default_executor() has been added to AbstractEventLoop , meaning alternative event loops that inherit from it should have this method defined. (Contributed by Kyle Stanley in bpo-34037 .)

• The constant values of future flags in the __future__ module is updated in order to prevent collision with compiler flags. Previously PyCF_ALLOW_TOP_LEVEL_AWAIT was clashing with CO_FUTURE_DIVISION . (Contributed by Batuhan Taskaya in bpo-39562 )

• array('u') now uses wchar_t as C type instead of Py_UNICODE . This change doesn’t affect to its behavior because Py_UNICODE is alias of wchar_t since Python 3.3. (Contributed by Inada Naoki in bpo-34538 .)

• logging.getLogger() API now returns the root logger when passed the name 'root' , whereas previously it returned a non-root logger named 'root' . This could affect cases where user code explicitly wants a non-root logger named 'root' , or instantiates a logger using logging.getLogger(__name__) in some top-level module called 'root.py' . (Contributed by Vinay Sajip in bpo-37742 .)

• Division handling of PurePath now returns NotImplemented instead of raising a TypeError when passed something other than an instance of str or PurePath . This allows creating compatible classes that don’t inherit from those mentioned types. (Contributed by Roger Aiudi in bpo-34775 ).

• Starting with Python 3.9.5 the ipaddress module no longer accepts any leading zeros in IPv4 address strings. Leading zeros are ambiguous and interpreted as octal notation by some libraries. For example the legacy function socket.inet_aton() treats leading zeros as octal notatation. glibc implementation of modern inet_pton() does not accept any leading zeros. (Contributed by Christian Heimes in bpo-36384 ).

• codecs.lookup() now normalizes the encoding name the same way as encodings.normalize_encoding() ，除了 codecs.lookup() also converts the name to lower case. For example, "latex+latin1" encoding name is now normalized to "latex_latin1" . (Contributed by Jordon Xu in bpo-37751 .)

C API 变化 ¶

• Instances of heap-allocated types (such as those created with PyType_FromSpec() and similar APIs) hold a reference to their type object since Python 3.8. As indicated in the “Changes in the C API” of Python 3.8, for the vast majority of cases, there should be no side effect but for types that have a custom tp_traverse function, ensure that all custom tp_traverse functions of heap-allocated types visit the object’s type.

  范例：

  int
  foo_traverse(foo_struct *self, visitproc visit, void *arg) {
  // Rest of the traverse function
  #if PY_VERSION_HEX >= 0x03090000
      // This was not needed before Python 3.9 (Python issue 35810 and 40217)
      Py_VISIT(Py_TYPE(self));
  #endif
  }
  													

  If your traverse function delegates to tp_traverse of its base class (or another type), ensure that Py_TYPE(self) is visited only once. Note that only heap types are expected to visit the type in tp_traverse .

  例如，若 tp_traverse 函数包括：

  base->tp_traverse(self, visit, arg)
  													

  then add:

  #if PY_VERSION_HEX >= 0x03090000
      // This was not needed before Python 3.9 (Python issue 35810 and 40217)
      if (base->tp_flags & Py_TPFLAGS_HEAPTYPE) {
          // a heap type's tp_traverse already visited Py_TYPE(self)
      } else {
          Py_VISIT(Py_TYPE(self));
      }
  #else
  													

  (见 bpo-35810 and bpo-40217 了解更多信息。)

• 函数 PyEval_CallObject , PyEval_CallFunction , PyEval_CallMethod and PyEval_CallObjectWithKeywords are deprecated. Use PyObject_Call() and its variants instead. (See more details in bpo-29548 .)

CPython 字节码变化 ¶

• LOAD_ASSERTION_ERROR opcode was added for handling the assert statement. Previously, the assert statement would not work correctly if the AssertionError exception was being shadowed. (Contributed by Zackery Spytz in bpo-34880 .)

• COMPARE_OP opcode was split into four distinct instructions:

  • COMPARE_OP for rich comparisons

  • IS_OP for ‘is’ and ‘is not’ tests

  • CONTAINS_OP for ‘in’ and ‘not in’ tests

  • JUMP_IF_NOT_EXC_MATCH for checking exceptions in ‘try-except’ statements.

  (Contributed by Mark Shannon in bpo-39156 .)

新特征 ¶

• PEP 573 ：添加 PyType_FromModuleAndSpec() to associate a module with a class; PyType_GetModule() and PyType_GetModuleState() to retrieve the module and its state; and PyCMethod and METH_METHOD to allow a method to access the class it was defined in. (Contributed by Marcel Plch and Petr Viktorin in bpo-38787 .)

• 添加 PyFrame_GetCode() function: get a frame code. Added PyFrame_GetBack() function: get the frame next outer frame. (Contributed by Victor Stinner in bpo-40421 .)

• 添加 PyFrame_GetLineNumber() to the limited C API. (Contributed by Victor Stinner in bpo-40421 .)

• 添加 PyThreadState_GetInterpreter() and PyInterpreterState_Get() functions to get the interpreter. Added PyThreadState_GetFrame() function to get the current frame of a Python thread state. Added PyThreadState_GetID() function: get the unique identifier of a Python thread state. (Contributed by Victor Stinner in bpo-39947 .)

• 添加新的公共 PyObject_CallNoArgs() function to the C API, which calls a callable Python object without any arguments. It is the most efficient way to call a callable Python object without any argument. (Contributed by Victor Stinner in bpo-37194 .)

• Changes in the limited C API (if Py_LIMITED_API macro is defined):

  • 提供 Py_EnterRecursiveCall() and Py_LeaveRecursiveCall() as regular functions for the limited API. Previously, there were defined as macros, but these macros didn’t compile with the limited C API which cannot access PyThreadState.recursion_depth field (the structure is opaque in the limited C API).

  • PyObject_INIT() and PyObject_INIT_VAR() become regular “opaque” function to hide implementation details.

  (Contributed by Victor Stinner in bpo-38644 and bpo-39542 .)

• PyModule_AddType() function is added to help adding a type to a module. (Contributed by Dong-hee Na in bpo-40024 .)

• Added the functions PyObject_GC_IsTracked() and PyObject_GC_IsFinalized() to the public API to allow to query if Python objects are being currently tracked or have been already finalized by the garbage collector respectively. (Contributed by Pablo Galindo Salgado in bpo-40241 .)

• 添加 _PyObject_FunctionStr() to get a user-friendly string representation of a function-like object. (Patch by Jeroen Demeyer in bpo-37645 .)

• 添加 PyObject_CallOneArg() for calling an object with one positional argument (Patch by Jeroen Demeyer in bpo-37483 .)

移植到 Python 3.9 ¶

• PyInterpreterState.eval_frame ( PEP 523 ) now requires a new mandatory tstate parameter ( PyThreadState* ). (Contributed by Victor Stinner in bpo-38500 .)

• Extension modules: m_traverse , m_clear and m_free functions of PyModuleDef are no longer called if the module state was requested but is not allocated yet. This is the case immediately after the module is created and before the module is executed ( Py_mod_exec function). More precisely, these functions are not called if m_size is greater than 0 and the module state (as returned by PyModule_GetState() ) is NULL .

  Extension modules without module state ( m_size <= 0 ) are not affected.

• 若 Py_AddPendingCall() is called in a subinterpreter, the function is now scheduled to be called from the subinterpreter, rather than being called from the main interpreter. Each subinterpreter now has its own list of scheduled calls. (Contributed by Victor Stinner in bpo-39984 .)

• The Windows registry is no longer used to initialize sys.path 当 -E option is used (if PyConfig.use_environment 被设为 0 ). This is significant when embedding Python on Windows. (Contributed by Zackery Spytz in bpo-8901 .)

• The global variable PyStructSequence_UnnamedField is now a constant and refers to a constant string. (Contributed by Serhiy Storchaka in bpo-38650 .)

• PyGC_Head structure is now opaque. It is only defined in the internal C API ( pycore_gc.h ). (Contributed by Victor Stinner in bpo-40241 .)

• Py_UNICODE_COPY , Py_UNICODE_FILL , PyUnicode_WSTR_LENGTH , PyUnicode_FromUnicode() , PyUnicode_AsUnicode() , _PyUnicode_AsUnicode ，和 PyUnicode_AsUnicodeAndSize() are marked as deprecated in C. They have been deprecated by PEP 393 since Python 3.3. (Contributed by Inada Naoki in bpo-36346 .)

• Py_FatalError() function is replaced with a macro which logs automatically the name of the current function, unless the Py_LIMITED_API macro is defined. (Contributed by Victor Stinner in bpo-39882 .)

• The vectorcall protocol now requires that the caller passes only strings as keyword names. (See bpo-37540 了解更多信息。)

• Implementation details of a number of macros and functions are now hidden:

  • PyObject_IS_GC() macro was converted to a function.

  • PyObject_NEW() macro becomes an alias to the PyObject_New() macro, and the PyObject_NEW_VAR() macro becomes an alias to the PyObject_NewVar() macro. They no longer access directly the PyTypeObject.tp_basicsize member.

  • PyType_HasFeature() 现在始终调用 PyType_GetFlags() . Previously, it accessed directly the PyTypeObject.tp_flags member when the limited C API was not used.

  • PyObject_GET_WEAKREFS_LISTPTR() macro was converted to a function: the macro accessed directly the PyTypeObject.tp_weaklistoffset member.

  • PyObject_CheckBuffer() macro was converted to a function: the macro accessed directly the PyTypeObject.tp_as_buffer member.

  • PyIndex_Check() is now always declared as an opaque function to hide implementation details: removed the PyIndex_Check() macro. The macro accessed directly the PyTypeObject.tp_as_number member.

  (见 bpo-40170 了解更多细节。)

移除 ¶

• 排除 PyFPE_START_PROTECT() and PyFPE_END_PROTECT() macros of pyfpe.h from the limited C API. (Contributed by Victor Stinner in bpo-38835 .)

• tp_print slot of PyTypeObject has been removed. It was used for printing objects to files in Python 2.7 and before. Since Python 3.0, it has been ignored and unused. (Contributed by Jeroen Demeyer in bpo-36974 .)

• Changes in the limited C API (if Py_LIMITED_API macro is defined):

  • Excluded the following functions from the limited C API:

    • PyThreadState_DeleteCurrent() (Contributed by Joannah Nanjekye in bpo-37878 .)

    • _Py_CheckRecursionLimit

    • _Py_NewReference()

    • _Py_ForgetReference()

    • _PyTraceMalloc_NewReference()

    • _Py_GetRefTotal()

    • The trashcan mechanism which never worked in the limited C API.

    • PyTrash_UNWIND_LEVEL

    • Py_TRASHCAN_BEGIN_CONDITION

    • Py_TRASHCAN_BEGIN

    • Py_TRASHCAN_END

    • Py_TRASHCAN_SAFE_BEGIN

    • Py_TRASHCAN_SAFE_END

  • Moved following functions and definitions to the internal C API:

    • _PyDebug_PrintTotalRefs()

    • _Py_PrintReferences()

    • _Py_PrintReferenceAddresses()

    • _Py_tracemalloc_config

    • _Py_AddToAllObjects() (specific to Py_TRACE_REFS build)

  (Contributed by Victor Stinner in bpo-38644 and bpo-39542 .)

• 移除 _PyRuntime.getframe hook and removed _PyThreadState_GetFrame macro which was an alias to _PyRuntime.getframe . They were only exposed by the internal C API. Removed also PyThreadFrameGetter type. (Contributed by Victor Stinner in bpo-39946 .)

• Removed the following functions from the C API. Call PyGC_Collect() explicitly to clear all free lists. (Contributed by Inada Naoki and Victor Stinner in bpo-37340 , bpo-38896 and bpo-40428 .)

  • PyAsyncGen_ClearFreeLists()

  • PyContext_ClearFreeList()

  • PyDict_ClearFreeList()

  • PyFloat_ClearFreeList()

  • PyFrame_ClearFreeList()

  • PyList_ClearFreeList()

  • PyMethod_ClearFreeList() and PyCFunction_ClearFreeList() : the free lists of bound method objects have been removed.

  • PySet_ClearFreeList() : the set free list has been removed in Python 3.4.

  • PyTuple_ClearFreeList()

  • PyUnicode_ClearFreeList() : the Unicode free list has been removed in Python 3.3.

• 移除 _PyUnicode_ClearStaticStrings() function. (Contributed by Victor Stinner in bpo-39465 .)

• 移除 Py_UNICODE_MATCH . It has been deprecated by PEP 393 , and broken since Python 3.3. The PyUnicode_Tailmatch() function can be used instead. (Contributed by Inada Naoki in bpo-36346 .)

• Cleaned header files of interfaces defined but with no implementation. The public API symbols being removed are: _PyBytes_InsertThousandsGroupingLocale , _PyBytes_InsertThousandsGrouping , _Py_InitializeFromArgs , _Py_InitializeFromWideArgs , _PyFloat_Repr , _PyFloat_Digits , _PyFloat_DigitsInit , PyFrame_ExtendStack , _PyAIterWrapper_Type , PyNullImporter_Type , PyCmpWrapper_Type , PySortWrapper_Type , PyNoArgsFunction . (Contributed by Pablo Galindo Salgado in bpo-39372 .)

typing ¶

行为在 typing.Literal was changed to conform with PEP 586 and to match the behavior of static type checkers specified in the PEP.

1. Literal now de-duplicates parameters.

2. Equality comparisons between Literal objects are now order independent.

3. Literal comparisons now respect types. For example, Literal[0] == Literal[False] previously evaluated to True . It is now False . To support this change, the internally used type cache now supports differentiating types.

4. Literal objects will now raise a TypeError exception during equality comparisons if any of their parameters are not hashable . Note that declaring Literal with mutable parameters will not throw an error:

   >>> from typing import Literal
   >>> Literal[{0}]
   >>> Literal[{0}] == Literal[{False}]
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: unhashable type: 'set'
   											

(Contributed by Yurii Karabas in bpo-42345 .)

macOS 11.0 (Big Sur) 和 Apple Silicon Mac 支持 ¶

As of 3.9.1, Python now fully supports building and running on macOS 11.0 (Big Sur) and on Apple Silicon Macs (based on the ARM64 architecture). A new universal build variant, universal2 , is now available to natively support both ARM64 and Intel 64 in one set of executables. Binaries can also now be built on current versions of macOS to be deployed on a range of older macOS versions (tested to 10.9) while making some newer OS functions and options conditionally available based on the operating system version in use at runtime (“weaklinking”).

(Contributed by Ronald Oussoren and Lawrence D’Anna in bpo-41100 .)

collections.abc ¶

collections.abc.Callable generic now flattens type parameters, similar to what typing.Callable currently does. This means that collections.abc.Callable[[int, str], str] will have __args__ of (int, str, str) ; previously this was ([int, str], str) . To allow this change, types.GenericAlias can now be subclassed, and a subclass will be returned when subscripting the collections.abc.Callable type. Code which accesses the arguments via typing.get_args() or __args__ need to account for this change. A DeprecationWarning may be emitted for invalid forms of parameterizing collections.abc.Callable which may have passed silently in Python 3.9.1. This DeprecationWarning will become a TypeError in Python 3.10. (Contributed by Ken Jin in bpo-42195 .)

urllib.parse ¶

Earlier Python versions allowed using both ; and & as query parameter separators in urllib.parse.parse_qs() and urllib.parse.parse_qsl() . Due to security concerns, and to conform with newer W3C recommendations, this has been changed to allow only a single separator key, with & as the default. This change also affects cgi.parse() and cgi.parse_multipart() as they use the affected functions internally. For more details, please see their respective documentation. (Contributed by Adam Goldschmidt, Senthil Kumaran and Ken Jin in bpo-42967 .)

urllib.parse ¶

The presence of newline or tab characters in parts of a URL allows for some forms of attacks. Following the WHATWG specification that updates RFC 3986 , ASCII newline \n , \r and tab \t characters are stripped from the URL by the parser in urllib.parse preventing such attacks. The removal characters are controlled by a new module level variable urllib.parse._UNSAFE_URL_BYTES_TO_REMOVE . (See bpo-43882 )