What’s New In Python 3.10¶
- Release
3.10.0a1
- Date
November 03, 2020
This article explains the new features in Python 3.10, compared to 3.9.
For full details, see the changelog.
Note
Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.10 moves towards release, so it’s worth checking back even after reading earlier versions.
Summary – Release highlights¶
New Features¶
PEP 563: Postponed Evaluation of Annotations Becomes Default¶
In Python 3.7, postponed evaluation of annotations was added,
to be enabled with a from __future__ import annotations
directive. In 3.10 this became the default behavior, even
without that future directive. With this being default, all
annotations stored in __annotations__
will be strings.
If needed, annotations can be resolved at runtime using
typing.get_type_hints()
. See PEP 563 for a full
description. Also, the inspect.signature()
will try to
resolve types from now on, and when it fails it will fall back to
showing the string annotations. (Contributed by Batuhan Taskaya
in bpo-38605.)
The
int
type has a new methodint.bit_count()
, returning the number of ones in the binary expansion of a given integer, also known as the population count. (Contributed by Niklas Fiekas in bpo-29882.)The views returned by
dict.keys()
,dict.values()
anddict.items()
now all have amapping
attribute that gives atypes.MappingProxyType
object wrapping the original dictionary. (Contributed by Dennis Sweeney in bpo-40890.)PEP 618: The
zip()
function now has an optionalstrict
flag, used to require that all the iterables have an equal length.
PEP 613: TypeAlias Annotation¶
PEP 484 introduced the concept of type aliases, only requiring them to be top-level unannotated assignments. This simplicity sometimes made it difficult for type checkers to distinguish between type aliases and ordinary assignments, especially when forward references or invalid types were involved. Compare:
StrCache = 'Cache[str]' # a type alias
LOG_PREFIX = 'LOG[DEBUG]' # a module constant
Now the typing
module has a special annotation TypeAlias
to
declare type aliases more explicitly:
StrCache: TypeAlias = 'Cache[str]' # a type alias
LOG_PREFIX = 'LOG[DEBUG]' # a module constant
See PEP 613 for more details.
(Contributed by Mikhail Golubev in bpo-41923.)
PEP604: New Type Union Operator¶
A new type union operator was introduced which enables the syntax X | Y
.
This provides a cleaner way of expressing ‘either type X or type Y’ instead of
using typing.Union
, especially in type hints (annotations).
In previous versions of Python, to apply a type hint for functions accepting
arguments of multiple types, typing.Union
was used:
def square(number: Union[int, float]) -> Union[int, float]:
return number ** 2
Type hints can now be written in a more succinct manner:
def square(number: int | float) -> int | float:
return number ** 2
See PEP 604 for more details.
(Contributed by Maggie Moss and Philippe Prados in bpo-41428.)
Other Language Changes¶
Builtin and extension functions that take integer arguments no longer accept
Decimal
s,Fraction
s and other objects that can be converted to integers only with a loss (e.g. that have the__int__()
method but do not have the__index__()
method). (Contributed by Serhiy Storchaka in bpo-37999.)
New Modules¶
None yet.
Improved Modules¶
base64¶
Add base64.b32hexencode()
and base64.b32hexdecode()
to support the
Base32 Encoding with Extended Hex Alphabet.
codecs¶
Add a codecs.unregister()
function to unregister a codec search function.
(Contributed by Hai Shi in bpo-41842.)
curses¶
The extended color functions added in ncurses 6.1 will be used transparently
by curses.color_content()
, curses.init_color()
,
curses.init_pair()
, and curses.pair_content()
. A new function,
curses.has_extended_color_support()
, indicates whether extended color
support is provided by the underlying ncurses library.
(Contributed by Jeffrey Kintscher and Hans Petter Jansson in bpo-36982.)
encodings¶
encodings.normalize_encoding()
now ignores non-ASCII characters.
(Contributed by Hai Shi in bpo-39337.)
glob¶
Added the root_dir and dir_fd parameters in glob()
and
iglob()
which allow to specify the root directory for searching.
(Contributed by Serhiy Storchaka in bpo-38144.)
os¶
Added os.cpu_count()
support for VxWorks RTOS.
(Contributed by Peixing Xin in bpo-41440.)
py_compile¶
Added --quiet
option to command-line interface of py_compile
.
(Contributed by Gregory Schevchenko in bpo-38731.)
shelve¶
The shelve
module now uses pickle.DEFAULT_PROTOCOL
by default
instead of pickle
protocol 3
when creating shelves.
(Contributed by Zackery Spytz in bpo-34204.)
sys¶
Add sys.orig_argv
attribute: the list of the original command line
arguments passed to the Python executable.
(Contributed by Victor Stinner in bpo-23427.)
types¶
Reintroduced the types.EllipsisType
, types.NoneType
and types.NotImplementedType
classes, providing a new set
of types readily interpretable by type checkers.
(Contributed by Bas van Beek in bpo-41810.)
unittest¶
Add new method assertNoLogs()
to complement the
existing assertLogs()
. (Contributed by Kit Yan Choi
in bpo-39385.)
xml¶
Add a LexicalHandler
class to the
xml.sax.handler
module.
(Contributed by Jonathan Gossage and Zackery Spytz in bpo-35018.)
Optimizations¶
Constructors
str()
,bytes()
andbytearray()
are now faster (around 30–40% for small objects). (Contributed by Serhiy Storchaka in bpo-41334.)The
runpy
module now imports fewer modules. Thepython3 -m module-name
command startup time is 1.3x faster in average. (Contributed by Victor Stinner in bpo-41006.)The
LOAD_ATTR
instruction now uses new “per opcode cache” mechanism. It is about 36% faster now. (Contributed by Pablo Galindo and Yury Selivanov in bpo-42093, based on ideas implemented originally in PyPy and MicroPython.)When building Python with
--enable-optimizations
now-fno-semantic-interposition
is added to both the compile and link line. This speeds builds of the Python interpreter created with--enable-shared
withgcc
by up to 30%. See this article for more details. (Contributed by Victor Stinner and Pablo Galindo in bpo-38980)
Deprecated¶
Starting in this release, there will be a concerted effort to begin cleaning up old import semantics that were kept for Python 2.7 compatibility. Specifically,
find_loader()
/find_module()
(superseded byfind_spec()
),load_module()
(superseded byexec_module()
),module_repr()
(which the import system takes care of for you), the__package__
attribute (superseded by__spec__.parent
), the__loader__
attribute (superseded by__spec__.loader
), and the__cached__
attribute (superseded by__spec__.cached
) will slowly be removed (as well as other classes and methods inimportlib
).ImportWarning
and/orDeprecationWarning
will be raised as appropriate to help identify code which needs updating during this transition.
Removed¶
Removed special methods
__int__
,__float__
,__floordiv__
,__mod__
,__divmod__
,__rfloordiv__
,__rmod__
and__rdivmod__
of thecomplex
class. They always raised aTypeError
. (Contributed by Serhiy Storchaka in bpo-41974.)The
ParserBase.error()
method from the private and undocumented_markupbase
module has been removed.html.parser.HTMLParser
is the only subclass ofParserBase
and itserror()
implementation has already been removed in Python 3.5. (Contributed by Berker Peksag in bpo-31844.)Removed the
unicodedata.ucnhash_CAPI
attribute which was an internal PyCapsule object. The related private_PyUnicode_Name_CAPI
structure was moved to the internal C API. (Contributed by Victor Stinner in bpo-42157.)
Porting to Python 3.10¶
This section lists previously described changes and other bugfixes that may require changes to your code.
Build Changes¶
C API Changes¶
New Features¶
The result of
PyNumber_Index()
now always has exact typeint
. Previously, the result could have been an instance of a subclass ofint
. (Contributed by Serhiy Storchaka in bpo-40792.)Add a new
orig_argv
member to thePyConfig
structure: the list of the original command line arguments passed to the Python executable. (Contributed by Victor Stinner in bpo-23427.)The
PyDateTime_DATE_GET_TZINFO()
andPyDateTime_TIME_GET_TZINFO()
macros have been added for accessing thetzinfo
attributes ofdatetime.datetime
anddatetime.time
objects. (Contributed by Zackery Spytz in bpo-30155.)Add a
PyCodec_Unregister()
function to unregister a codec search function. (Contributed by Hai Shi in bpo-41842.)The
PyIter_Send()
function was added to allow sending value into iterator without raisingStopIteration
exception. (Contributed by Vladimir Matveev in bpo-41756.)Added
PyUnicode_AsUTF8AndSize()
to the limited C API. (Contributed by Alex Gaynor in bpo-41784.)
Porting to Python 3.10¶
The
PY_SSIZE_T_CLEAN
macro must now be defined to usePyArg_ParseTuple()
andPy_BuildValue()
formats which use#
:es#
,et#
,s#
,u#
,y#
,z#
,U#
andZ#
. See Parsing arguments and building values and the PEP 353. (Contributed by Victor Stinner in bpo-40943.)Since
Py_TYPE()
is changed to the inline static function,Py_TYPE(obj) = new_type
must be replaced withPy_SET_TYPE(obj, new_type)
: seePy_SET_TYPE()
(available since Python 3.9). For backward compatibility, this macro can be used:#if PY_VERSION_HEX < 0x030900A4 # define Py_SET_TYPE(obj, type) ((Py_TYPE(obj) = (type)), (void)0) #endif
(Contributed by Dong-hee Na in bpo-39573.)
Since
Py_REFCNT()
is changed to the inline static function,Py_REFCNT(obj) = new_refcnt
must be replaced withPy_SET_REFCNT(obj, new_refcnt)
: seePy_SET_REFCNT()
(available since Python 3.9). For backward compatibility, this macro can be used:#if PY_VERSION_HEX < 0x030900A4 # define Py_SET_REFCNT(obj, refcnt) ((Py_REFCNT(obj) = (refcnt)), (void)0) #endif
(Contributed by Victor Stinner in bpo-39573.)
Since
Py_SIZE()
is changed to the inline static function,Py_SIZE(obj) = new_size
must be replaced withPy_SET_SIZE(obj, new_size)
: seePy_SET_SIZE()
(available since Python 3.9). For backward compatibility, this macro can be used:#if PY_VERSION_HEX < 0x030900A4 # define Py_SET_SIZE(obj, size) ((Py_SIZE(obj) = (size)), (void)0) #endif
(Contributed by Victor Stinner in bpo-39573.)
Calling
PyDict_GetItem()
without GIL held had been allowed for historical reason. It is no longer allowed. (Contributed by Victor Stinner in bpo-40839.)PyUnicode_FromUnicode(NULL, size)
andPyUnicode_FromStringAndSize(NULL, size)
raiseDeprecationWarning
now. UsePyUnicode_New()
to allocate Unicode object without initial data. (Contributed by Inada Naoki in bpo-36346.)The private
_PyUnicode_Name_CAPI
structure of the PyCapsule APIunicodedata.ucnhash_CAPI
has been moved to the internal C API. (Contributed by Victor Stinner in bpo-42157.)
Deprecated¶
The
PyUnicode_InternImmortal()
function is now deprecated and will be removed in Python 3.12: usePyUnicode_InternInPlace()
instead. (Contributed by Victor Stinner in bpo-41692.)
Removed¶
PyObject_AsCharBuffer()
,PyObject_AsReadBuffer()
,PyObject_CheckReadBuffer()
, andPyObject_AsWriteBuffer()
are removed. Please migrate to new buffer protocol;PyObject_GetBuffer()
andPyBuffer_Release()
. (Contributed by Inada Naoki in bpo-41103.)Removed
Py_UNICODE_str*
functions manipulatingPy_UNICODE*
strings. (Contributed by Inada Naoki in bpo-41123.)Py_UNICODE_strlen
: usePyUnicode_GetLength()
orPyUnicode_GET_LENGTH
Py_UNICODE_strcat
: usePyUnicode_CopyCharacters()
orPyUnicode_FromFormat()
Py_UNICODE_strcpy
,Py_UNICODE_strncpy
: usePyUnicode_CopyCharacters()
orPyUnicode_Substring()
Py_UNICODE_strcmp
: usePyUnicode_Compare()
Py_UNICODE_strncmp
: usePyUnicode_Tailmatch()
Py_UNICODE_strchr
,Py_UNICODE_strrchr
: usePyUnicode_FindChar()
Removed
PyUnicode_GetMax()
. Please migrate to new (PEP 393) APIs. (Contributed by Inada Naoki in bpo-41103.)Removed
PyLong_FromUnicode()
. Please migrate toPyLong_FromUnicodeObject()
. (Contributed by Inada Naoki in bpo-41103.)Removed
PyUnicode_AsUnicodeCopy()
. Please usePyUnicode_AsUCS4Copy()
orPyUnicode_AsWideCharString()
(Contributed by Inada Naoki in bpo-41103.)Removed
_Py_CheckRecursionLimit
variable: it has been replaced byceval.recursion_limit
of thePyInterpreterState
structure. (Contributed by Victor Stinner in bpo-41834.)Removed undocumented macros
Py_ALLOW_RECURSION
andPy_END_ALLOW_RECURSION
and therecursion_critical
field of thePyInterpreterState
structure. (Contributed by Serhiy Storchaka in bpo-41936.)