What's New In Python 3.9¶
- 发布版本
3.9.0b2
- Date
六月 09, 2020
This article explains the new features in Python 3.9, compared to 3.8.
For full details, see the changelog.
注解
Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.9 moves towards release, so it's worth checking back even after reading earlier versions.
摘要 - 发布重点¶
You should check for DeprecationWarning in your code¶
When Python 2.7 was still supported, many functions were kept for backward
compatibility with Python 2.7. With the end of Python 2.7 support, these
backward compatibility layers have been removed, or will be removed soon.
Most of them emitted a DeprecationWarning
warning for several years. For
example, using collections.Mapping
instead of collections.abc.Mapping
emits a DeprecationWarning
since Python 3.3, released in 2012.
Test your application with the -W
default
command-line option to see
DeprecationWarning
and PendingDeprecationWarning
, or even with
-W
error
to treat them as errors. Warnings Filter can be used to ignore warnings from third-party code.
It has been decided to keep a few backward compatibility layers for one last release, to give more time to Python projects maintainers to organize the removal of the Python 2 support and add support for Python 3.9.
Aliases to Abstract Base Classes in
the collections
module, like collections.Mapping
alias to
collections.abc.Mapping
, are kept for one last release for backward
compatibility. They will be removed from Python 3.10.
More generally, try to run your tests in the Python Development Mode which helps to prepare your code to make it compatible with the next Python version.
新的特性¶
Dictionary Merge & Update Operators¶
Merge (|
) and update (|=
) operators have been added to the built-in
dict
class. See PEP 584 for a full description.
(Contributed by Brandt Bucher in bpo-36144.)
PEP 616: New removeprefix() and removesuffix() string methods¶
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
, and collections.UserString
methods have also been
added. See PEP 616 for a full description. (Contributed by Dennis Sweeney in
bpo-39939.)
PEP 585: Builtin Generic Types¶
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
.
示例:
def greet_all(names: list[str]) -> None:
for name in names:
print("Hello", name)
See PEP 585 for more details. (Contributed by Guido van Rossum, Ethan Smith, and Batuhan Taşkaya in bpo-39481.)
PEP 617: New Parser¶
Python 3.9 uses a new parser, based on PEG instead of 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.
The 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
).
See PEP 617 for more details. (Contributed by Guido van Rossum, Pablo Galindo and Lysandros Nikolaou in bpo-40334.)
其他语言特性修改¶
__import__()
now raisesImportError
instead ofValueError
, which used to occur when a relative import went past its top-level package. (Contributed by Ngalim Siregar in bpo-37444.)Python now gets the absolute path of the script filename specified on the command line (ex:
python3 script.py
): the__file__
attribute of the__main__
module became an absolute path, rather than a relative path. These paths now remain valid after the current directory is changed byos.chdir()
. As a side effect, the traceback also displays the absolute path for__main__
module frames in this case. (Contributed by Victor Stinner in bpo-20443.)In the Python Development Mode and in debug build, the encoding and errors arguments are now checked for string encoding and decoding operations. Examples:
open()
,str.encode()
andbytes.decode()
.By default, for best performance, the errors argument is only checked at the first encoding/decoding error and the encoding argument is sometimes ignored for empty strings. (Contributed by Victor Stinner in bpo-37388.)
"".replace("", s, n)
now returnss
instead of an empty string for all non-zeron
. It is now consistent with"".replace("", s)
. There are similar changes forbytes
andbytearray
objects. (Contributed by Serhiy Storchaka in bpo-28029.)Any valid expression can now be used as a decorator. Previously, the grammar was much more restrictive. See PEP 614 for details. (Contributed by Brandt Bucher in bpo-39702.)
Improved help for the
typing
module. Docstrings are now shown for all special forms and special generic aliases (likeUnion
andList
). Usinghelp()
with generic alias likeList[int]
will show the help for the correspondent concrete type (list
in this case). (Contributed by Serhiy Storchaka in bpo-40257.)
新增模块¶
zoneinfo¶
The 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.
示例:
>>> 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.
参见
- PEP 615 -- Support for the IANA Time Zone Database in the Standard Library
PEP written and implemented by Paul Ganssle
graphlib¶
Add the graphlib
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.)
改进的模块¶
ast¶
Added the indent option to dump()
which allows it to produce a
multiline indented output.
(Contributed by Serhiy Storchaka in bpo-37995.)
Added 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¶
出于重要的安全性考量,asyncio.loop.create_datagram_endpoint()
的 reuse_address 形参不再被支持。 这是由 UDP 中的套接字选项 SO_REUSEADDR
的行为导致的。 更多细节请参阅 loop.create_datagram_endpoint()
的文档。 (由 Kyle Stanley, Antoine Pitrou 和 Yury Selivanov 在 bpo-37228 中贡献。。)
Added a new coroutine 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 coroutine.
(Contributed by Kyle Stanley in bpo-34037.)
Added asyncio.PidfdChildWatcher
, a Linux-specific child watcher
implementation that polls process file descriptors. (bpo-38692)
Added a new coroutine 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.)
compileall¶
Added new possibility to use hardlinks for duplicated .pyc
files: 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
files: 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¶
Added a new cancel_futures parameter to
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¶
Add curses.get_escdelay()
, curses.set_escdelay()
,
curses.get_tabsize()
, and curses.set_tabsize()
functions.
(Contributed by Anthony Sottile in bpo-38312.)
datetime¶
The isocalendar()
of datetime.date
and isocalendar()
of datetime.datetime
methods now returns a namedtuple()
instead of a tuple
.
(Contributed by Dong-hee Na in bpo-24416.)
distutils¶
The 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¶
Added constants F_OFD_GETLK
, F_OFD_SETLK
and F_OFD_SETLKW
.
(Contributed by Dong-hee Na in bpo-38602.)
ftplib¶
FTP
and FTP_TLS
now raise a 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.)
Added a new function gc.is_finalized()
to check if an object has been
finalized by the garbage collector. (Contributed by Pablo Galindo in
bpo-39322.)
hashlib¶
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 status codes 103 EARLY_HINTS
, 418 IM_A_TEAPOT
and 425 TOO_EARLY
are added to
http.HTTPStatus
. (Contributed by Dong-hee Na in bpo-39509 and Ross Rhodes in bpo-39507.)
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()
now raises ImportError
instead of ValueError
for invalid relative
import attempts.
(Contributed by Ngalim Siregar in bpo-37444.)
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.)
math¶
Expanded the math.gcd()
function to handle multiple arguments.
Formerly, it only supported two arguments.
(Contributed by Serhiy Storchaka in bpo-39648.)
Add math.lcm()
: return the least common multiple of specified arguments.
(Contributed by Mark Dickinson, Ananthakrishnan and Serhiy Storchaka in
bpo-39479 and bpo-39648.)
Add math.nextafter()
: return the next floating-point value after x
towards y.
(Contributed by Victor Stinner in bpo-39288.)
Add math.ulp()
: return the value of the least significant bit
of a float.
(Contributed by Victor Stinner in bpo-39310.)
multiprocessing¶
The 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
now raise a 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¶
Added CLD_KILLED
and CLD_STOPPED
for si_code
.
(Contributed by Dong-hee Na in bpo-38493.)
Exposed the Linux-specific os.pidfd_open()
(bpo-38692) and
os.P_PIDFD
(bpo-38713) for process management with file
descriptors.
The os.unsetenv()
function is now also available on Windows.
(Contributed by Victor Stinner in bpo-39413.)
The os.putenv()
and os.unsetenv()
functions are now always
available.
(Contributed by Victor Stinner in bpo-39395.)
Add os.waitstatus_to_exitcode()
function:
convert a wait status to an exit code.
(Contributed by Victor Stinner in bpo-40094.)
pathlib¶
Added pathlib.Path.readlink()
which acts similarly to
os.readlink()
.
(Contributed by Girts Folkmanis in bpo-30618)
poplib¶
POP3
and POP3_SSL
now raise a 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¶
Add a new 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
now raise a 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¶
The 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.)
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¶
Add a new 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.)
Previously, sys.stderr
was block-buffered when non-interactive. Now
stderr
defaults to always being line-buffered.
(Contributed by Jendrik Seipp in bpo-13601.)
tracemalloc¶
Added 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
parameter to
typing.get_type_hints()
to access the metadata at runtime. (Contributed
by Till Varoquaux and Konstantin Kashin.)
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.)
性能优化¶
Optimized the idiom for assignment a temporary variable in comprehensions. Now
for y in [expr]
in comprehensions is as fast as a simple assignmenty = expr
. For example:sums = [s for s in [0] for x in data for s in [s + x]]
Unlike the
:=
operator this idiom does not leak a variable to the outer scope.(Contributed by Serhiy Storchaka in bpo-32856.)
Optimize signal handling in multithreaded applications. If a thread different than the main thread gets a signal, the bytecode evaluation loop is no longer interrupted at each bytecode instruction to check for pending signals which cannot be handled. Only the main thread of the main interpreter can handle signals.
Previously, the bytecode evaluation loop was interrupted at each instruction until the main thread handles signals. (Contributed by Victor Stinner in bpo-40010.)
Optimize the
subprocess
module on FreeBSD usingclosefrom()
. (Contributed by Ed Maste, Conrad Meyer, Kyle Evans, Kubilay Kocak and Victor Stinner in bpo-38061.)
Here's a summary of performance improvements from Python 3.4 through Python 3.9:
Python version 3.4 3.5 3.6 3.7 3.8 3.9
-------------- --- --- --- --- --- ---
Variable and attribute read access:
read_local 7.1 7.1 5.4 5.1 3.9 4.0
read_nonlocal 7.1 8.1 5.8 5.4 4.4 4.8
read_global 15.5 19.0 14.3 13.6 7.6 7.7
read_builtin 21.1 21.6 18.5 19.0 7.5 7.7
read_classvar_from_class 25.6 26.5 20.7 19.5 18.4 18.6
read_classvar_from_instance 22.8 23.5 18.8 17.1 16.4 20.1
read_instancevar 32.4 33.1 28.0 26.3 25.4 27.7
read_instancevar_slots 27.8 31.3 20.8 20.8 20.2 24.5
read_namedtuple 73.8 57.5 45.0 46.8 18.4 23.2
read_boundmethod 37.6 37.9 29.6 26.9 27.7 45.9
Variable and attribute write access:
write_local 8.7 9.3 5.5 5.3 4.3 4.2
write_nonlocal 10.5 11.1 5.6 5.5 4.7 4.9
write_global 19.7 21.2 18.0 18.0 15.8 17.2
write_classvar 92.9 96.0 104.6 102.1 39.2 43.2
write_instancevar 44.6 45.8 40.0 38.9 35.5 40.7
write_instancevar_slots 35.6 36.1 27.3 26.6 25.7 27.7
Data structure read access:
read_list 24.2 24.5 20.8 20.8 19.0 21.1
read_deque 24.7 25.5 20.2 20.6 19.8 21.6
read_dict 24.3 25.7 22.3 23.0 21.0 22.5
read_strdict 22.6 24.3 19.5 21.2 18.9 21.6
Data structure write access:
write_list 27.1 28.5 22.5 21.6 20.0 21.6
write_deque 28.7 30.1 22.7 21.8 23.5 23.2
write_dict 31.4 33.3 29.3 29.2 24.7 27.8
write_strdict 28.4 29.9 27.5 25.2 23.1 29.8
Stack (or queue) operations:
list_append_pop 93.4 112.7 75.4 74.2 50.8 53.9
deque_append_pop 43.5 57.0 49.4 49.2 42.5 45.5
deque_append_popleft 43.7 57.3 49.7 49.7 42.8 45.5
Timing loop:
loop_overhead 0.5 0.6 0.4 0.3 0.3 0.3
These results were generated from the variable access benchmark script at:
Tools/scripts/var_access_benchmark.py
. The benchmark script displays timings
in nanoseconds. The benchmarks were measured on an
Intel® Core™ i7-4960HQ processor
running the macOS 64-bit builds found at
python.org.
弃用¶
The distutils
bdist_msi
command is now deprecated, usebdist_wheel
(wheel packages) instead. (Contributed by Hugo van Kemenade in bpo-39586.)Currently
math.factorial()
acceptsfloat
instances with non-negative integer values (like5.0
). It raises aValueError
for non-integral and negative floats. It is now deprecated. In future Python versions it will raise aTypeError
for all floats. (Contributed by Serhiy Storchaka in bpo-37315.)The
parser
andsymbol
modules are deprecated and will be removed in future versions of Python. For the majority of use cases, users can leverage the Abstract Syntax Tree (AST) generation and compilation stage, using theast
module.Using
NotImplemented
in a boolean context has been deprecated, as it is almost exclusively the result of incorrect rich comparator implementations. It will be made aTypeError
in a future version of Python. (Contributed by Josh Rosenberg in bpo-35712.)The
random
module currently accepts any hashable type as a possible seed value. Unfortunately, some of those types are not guaranteed to have a deterministic hash value. After Python 3.9, the module will restrict its seeds toNone
,int
,float
,str
,bytes
, andbytearray
.Opening the
GzipFile
file for writing without specifying the mode argument is deprecated. In future Python versions it will always be opened for reading by default. Specify the mode argument for opening it for writing and silencing a warning. (Contributed by Serhiy Storchaka in bpo-28286.)Deprecated the
split()
method of_tkinter.TkappType
in favour of thesplitlist()
method which has more consistent and predicable behavior. (Contributed by Serhiy Storchaka in bpo-38371.)The explicit passing of coroutine objects to
asyncio.wait()
has been deprecated and will be removed in version 3.11. (Contributed by Yury Selivanov and Kyle Stanley in bpo-34790.)binhex4 and hexbin4 standards are now deprecated. The
binhex
module and the followingbinascii
functions are now deprecated:(Contributed by Victor Stinner in bpo-39353.)
ast
classesslice
,Index
andExtSlice
are considered deprecated and will be removed in future Python versions.value
itself should be used instead ofIndex(value)
.Tuple(slices, Load())
should be used instead ofExtSlice(slices)
. (Contributed by Serhiy Storchaka in bpo-32892.)ast
classesSuite
,Param
,AugLoad
andAugStore
are considered deprecated and will be removed in future Python versions. They were not generated by the parser and not accepted by the code generator in Python 3. (Contributed by Batuhan Taskaya in bpo-39639 and bpo-39969 and Serhiy Storchaka in bpo-39988.)The
PyEval_InitThreads()
andPyEval_ThreadsInitialized()
functions are now deprecated and will be removed in Python 3.11. CallingPyEval_InitThreads()
now does nothing. The GIL is initialized byPy_Initialize()
since Python 3.7. (Contributed by Victor Stinner in bpo-39877.)Passing
None
as the first argument to theshlex.split()
function has been deprecated. (Contributed by Zackery Spytz in bpo-33262.)The
lib2to3
module now emits aPendingDeprecationWarning
. Python 3.9 switched to a PEG parser (see PEP 617), and Python 3.10 may include new language syntax that is not parsable by lib2to3's LL(1) parser. Thelib2to3
module may be removed from the standard library in a future Python version. Consider third-party alternatives such as LibCST or parso. (Contributed by Carl Meyer in bpo-40360.)The random parameter of
random.shuffle()
has been deprecated. (Contributed by Raymond Hettinger in bpo-40465)
移除¶
The erroneous version at
unittest.mock.__version__
has been removed.nntplib.NNTP
:xpath()
andxgtitle()
methods have been removed. These methods are deprecated since Python 3.3. Generally, these extensions are not supported or not enabled by NNTP server administrators. Forxgtitle()
, please usenntplib.NNTP.descriptions()
ornntplib.NNTP.description()
instead. (Contributed by Dong-hee Na in bpo-39366.)array.array
:tostring()
andfromstring()
methods have been removed. They were aliases totobytes()
andfrombytes()
, deprecated since Python 3.2. (Contributed by Victor Stinner in bpo-38916.)The undocumented
sys.callstats()
function has been removed. Since Python 3.7, it was deprecated and always returnedNone
. It required a special build optionCALL_PROFILE
which was already removed in Python 3.7. (Contributed by Victor Stinner in bpo-37414.)The
sys.getcheckinterval()
andsys.setcheckinterval()
functions have been removed. They were deprecated since Python 3.2. Usesys.getswitchinterval()
andsys.setswitchinterval()
instead. (Contributed by Victor Stinner in bpo-37392.)The C function
PyImport_Cleanup()
has been removed. It was documented as: "Empty the module table. For internal use only." (Contributed by Victor Stinner in bpo-36710.)_dummy_thread
anddummy_threading
modules have been removed. These modules were deprecated since Python 3.7 which requires threading support. (Contributed by Victor Stinner in bpo-37312.)aifc.openfp()
alias toaifc.open()
,sunau.openfp()
alias tosunau.open()
, andwave.openfp()
alias towave.open()
have been removed. They were deprecated since Python 3.7. (Contributed by Victor Stinner in bpo-37320.)The
isAlive()
method ofthreading.Thread
has been removed. It was deprecated since Python 3.8. Useis_alive()
instead. (Contributed by Dong-hee Na in bpo-37804.)Methods
getchildren()
andgetiterator()
of classesElementTree
andElement
in theElementTree
module have been removed. They were deprecated in Python 3.2. Useiter(x)
orlist(x)
instead ofx.getchildren()
andx.iter()
orlist(x.iter())
instead ofx.getiterator()
. Thexml.etree.cElementTree
module has been removed, use thexml.etree.ElementTree
module instead. Since Python 3.3 thexml.etree.cElementTree
module has been deprecated, thexml.etree.ElementTree
module uses a fast implementation whenever available. (Contributed by Serhiy Storchaka in bpo-36543.)The old
plistlib
API has been removed, it was deprecated since Python 3.4. Use theload()
,loads()
,dump()
, anddumps()
functions. Additionally, the use_builtin_types parameter was removed, standardbytes
objects are always used instead. (Contributed by Jon Janzen in bpo-36409.)The C function
PyGen_NeedsFinalizing
has been removed. It was not documented, tested, or used anywhere within CPython after the implementation of PEP 442. Patch by Joannah Nanjekye. (Contributed by Joannah Nanjekye in bpo-15088)base64.encodestring()
andbase64.decodestring()
, aliases deprecated since Python 3.1, have been removed: usebase64.encodebytes()
andbase64.decodebytes()
instead. (Contributed by Victor Stinner in bpo-39351.)fractions.gcd()
function has been removed, it was deprecated since Python 3.5 (bpo-22486): usemath.gcd()
instead. (Contributed by Victor Stinner in bpo-39350.)The buffering parameter of
bz2.BZ2File
has been removed. Since Python 3.0, it was ignored and using it emitted aDeprecationWarning
. Pass an open file object to control how the file is opened. (Contributed by Victor Stinner in bpo-39357.)The encoding parameter of
json.loads()
has been removed. As of Python 3.1, it was deprecated and ignored; using it has emitted aDeprecationWarning
since Python 3.8. (Contributed by Inada Naoki in bpo-39377)with (await asyncio.lock):
andwith (yield from asyncio.lock):
statements are not longer supported, useasync with lock
instead. The same is correct forasyncio.Condition
andasyncio.Semaphore
. (Contributed by Andrew Svetlov in bpo-34793.)The
sys.getcounts()
function, the-X showalloccount
command line option and theshow_alloc_count
field of the C structurePyConfig
have been removed. They required a special Python build by definingCOUNT_ALLOCS
macro. (Contributed by Victor Stinner in bpo-39489.)The
_field_types
attribute of thetyping.NamedTuple
class has been removed. It was deprecated deprecated since Python 3.8. Use the__annotations__
attribute instead. (Contributed by Serhiy Storchaka in bpo-40182.)The
symtable.SymbolTable.has_exec()
method has been removed. It was deprecated since 2006, and only returningFalse
when it's called. (Contributed by Batuhan Taskaya in bpo-40208)
Porting to Python 3.9¶
本节列出了先前描述的更改以及可能需要更改代码的其他错误修正.
Python API 的变化¶
__import__()
andimportlib.util.resolve_name()
now raiseImportError
where it previously raisedValueError
. Callers catching the specific exception type and supporting both Python 3.9 and earlier versions will need to catch both usingexcept (ImportError, ValueError):
.The
venv
activation scripts no longer special-case when__VENV_PROMPT__
is set to""
.The
select.epoll.unregister()
method no longer ignores theEBADF
error. (Contributed by Victor Stinner in bpo-39239.)The 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 avalue
itself,ExtSlice(slices)
will returnTuple(slices, Load())
. (Contributed by Serhiy Storchaka in bpo-34822.)The
importlib
module now ignores thePYTHONCASEOK
environment variable when the-E
or-I
command line options are being used.The encoding parameter has been added to the classes
ftplib.FTP
andftplib.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 toAbstractEventLoop
, 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. PreviouslyPyCF_ALLOW_TOP_LEVEL_AWAIT
was clashing withCO_FUTURE_DIVISION
. (Contributed by Batuhan Taskaya in bpo-39562)array('u')
now useswchar_t
as C type instead ofPy_UNICODE
. This change doesn't affect to its behavior becausePy_UNICODE
is alias ofwchar_t
since Python 3.3. (Contributed by Inada Naoki in bpo-34538.)
C API 的变化¶
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 customtp_traverse
function, ensure that all customtp_traverse
functions of heap-allocated types visit the object's type.示例:
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 thatPy_TYPE(self)
is visited only once. Note that only heap types are expected to visit the type intp_traverse
.For example, if your
tp_traverse
function includes: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
CPython 字节码的改变¶
The
LOAD_ASSERTION_ERROR
opcode was added for handling theassert
statement. Previously, the assert statement would not work correctly if theAssertionError
exception was being shadowed. (Contributed by Zackery Spytz in bpo-34880.)
构建的改变¶
Add
--with-platlibdir
option to theconfigure
script: name of the platform-specific library directory, stored in the newsys.platlibdir
attribute. Seesys.platlibdir
attribute for more information. (Contributed by Jan Matějek, Matěj Cepl, Charalampos Stratakis and Victor Stinner in bpo-1294959.)The
COUNT_ALLOCS
special build macro has been removed. (Contributed by Victor Stinner in bpo-39489.)On non-Windows platforms, the
setenv()
andunsetenv()
functions are now required to build Python. (Contributed by Victor Stinner in bpo-39395.)
C API 的改变¶
新的特性¶
Add
PyFrame_GetCode()
function: get a frame code. AddPyFrame_GetBack()
function: get the frame next outer frame. (Contributed by Victor Stinner in bpo-40421.)Add
PyFrame_GetLineNumber()
to the limited C API. (Contributed by Victor Stinner in bpo-40421.)Add
PyThreadState_GetInterpreter()
andPyInterpreterState_Get()
functions to get the interpreter. AddPyThreadState_GetFrame()
function to get the current frame of a Python thread state. AddPyThreadState_GetID()
function: get the unique identifier of a Python thread state. (Contributed by Victor Stinner in bpo-39947.)Add a new public
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):Provide
Py_EnterRecursiveCall()
andPy_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 accessPyThreadState.recursion_depth
field (the structure is opaque in the limited C API).PyObject_INIT()
andPyObject_INIT_VAR()
become regular "opaque" function to hide implementation details.
The
PyModule_AddType()
function is added to help adding a type to a module. (Contributed by Dong-hee Na in bpo-40024.)Add the functions
PyObject_GC_IsTracked()
andPyObject_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 in bpo-40241.)
Porting to 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
andm_free
functions ofPyModuleDef
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 ifm_size
is greater than 0 and the module state (as returned byPyModule_GetState()
) isNULL
.Extension modules without module state (
m_size <= 0
) are not affected.If
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
when the-E
option is used (ifPyConfig.use_environment
is set to0
). 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.)The
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.)
移除¶
Exclude
PyFPE_START_PROTECT()
andPyFPE_END_PROTECT()
macros ofpyfpe.h
from the limited C API. (Contributed by Victor Stinner in bpo-38835.)The
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):Exclude 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
Move following functions and definitions to the internal C API:
_PyDebug_PrintTotalRefs()
_Py_PrintReferences()
_Py_PrintReferenceAddresses()
_Py_tracemalloc_config
_Py_AddToAllObjects()
(specific toPy_TRACE_REFS
build)
Remove
_PyRuntime.getframe
hook and remove_PyThreadState_GetFrame
macro which was an alias to_PyRuntime.getframe
. They were only exposed by the internal C API. Remove alsoPyThreadFrameGetter
type. (Contributed by Victor Stinner in bpo-39946.)Remove 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()
andPyCFunction_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.
Remove
_PyUnicode_ClearStaticStrings()
function. (Contributed by Victor Stinner in bpo-39465.)