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.. _python_39:
Python 3.9
==========
Python 3.9.0 (final) was released on the 5th October 2020. The Features for 3.9 are
defined in `PEP 596 <https://www.python.org/dev/peps/pep-0596/#features-for-3-9>`_
and a detailed description of the changes can be found in
`What's New in Python 3.9 <https://docs.python.org/3/whatsnew/3.9.html>`_
.. table::
:widths: 20 60 20
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| **Features** | | **Status** |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| `PEP 573 <https://www.python.org/dev/peps/pep-0573/>`_ | Fast access to module state from methods of C | Not relevant |
| | extension types | |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| `PEP 584 <https://www.python.org/dev/peps/pep-0584/>`_ | Union operators added to dict | Complete [#pep584]_ |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| `PEP 585 <https://www.python.org/dev/peps/pep-0584/>`_ | Type hinting generics in standard collections | |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| `PEP 593 <https://www.python.org/dev/peps/pep-0593/>`_ | Flexible function and variable annotations | |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| `PEP 602 <https://www.python.org/dev/peps/pep-0602/>`_ | CPython adopts an annual release cycle. Instead of | Not relevant |
| | annual, aiming for two month release cycle | |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| `PEP 614 <https://www.python.org/dev/peps/pep-0614/>`_ | Relaxed grammar restrictions on decorators | |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| `PEP 615 <https://www.python.org/dev/peps/pep-0615/>`_ | The IANA Time Zone Database is now present in the | |
| | standard library in the zoneinfo module | |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| `PEP 616 <https://www.python.org/dev/peps/pep-0616/>`_ | String methods to remove prefixes and suffixes | |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
| `PEP 617 <https://www.python.org/dev/peps/pep-0617/>`_ | CPython now uses a new parser based on PEG | Not relevant |
+--------------------------------------------------------+----------------------------------------------------+----------------------+
Other Language Changes:
.. table::
:widths: 90 10
+-------------------------------------------------------------------------------------------------------------+---------------+
| *__import__()* now raises *ImportError* instead of *ValueError* | Complete |
+-------------------------------------------------------------------------------------------------------------+---------------+
| 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 | |
+-------------------------------------------------------------------------------------------------------------+---------------+
| 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 | |
+-------------------------------------------------------------------------------------------------------------+---------------+
| *"".replace("", s, n)* now returns *s* instead of an empty string for all non-zero n. It is now consistent | |
| with *"".replace("", s)* | |
+-------------------------------------------------------------------------------------------------------------+---------------+
| Any valid expression can now be used as a decorator. Previously, the grammar was much more restrictive | |
+-------------------------------------------------------------------------------------------------------------+---------------+
| Parallel running of *aclose()* / *asend()* / *athrow()* is now prohibited, and *ag_running* now reflects | |
| the actual running status of the async generator | |
+-------------------------------------------------------------------------------------------------------------+---------------+
| Unexpected errors in calling the *__iter__* method are no longer masked by TypeError in the in operator and | |
| functions contains(), indexOf() and countOf() of the operator module | |
+-------------------------------------------------------------------------------------------------------------+---------------+
| Unparenthesized lambda expressions can no longer be the expression part in an if clause in comprehensions | |
| and generator expressions | |
+-------------------------------------------------------------------------------------------------------------+---------------+
Changes to built-in modules:
.. table::
:widths: 90 10
+---------------------------------------------------------------------------------------------------------------+---------------+
| `asyncio <https://docs.python.org/3/whatsnew/3.9.html#asyncio>`_ |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Due to significant security concerns, the reuse_address parameter of *asyncio.loop.create_datagram_endpoint()*| |
| is no longer supported | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| 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. | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Added *asyncio.PidfdChildWatcher*, a Linux-specific child watcher implementation that polls process file | |
| descriptors | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| added a new *coroutine asyncio.to_thread()* | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| 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 | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| *asyncio* now raises *TyperError* when calling incompatible methods with an *ssl.SSLSocket* socket | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| `gc <https://docs.python.org/3/whatsnew/3.9.html#gc>`_ |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Garbage collection does not block on resurrected objects | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Added a new function *gc.is_finalized()* to check if an object has been finalized by the garbage collector | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| `math <https://docs.python.org/3/whatsnew/3.9.html#math>`_ |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Expanded the *math.gcd()* function to handle multiple arguments. Formerly, it only supported two arguments | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Added *math.lcm()*: return the least common multiple of specified arguments | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Added *math.nextafter()*: return the next floating-point value after x towards y | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Added *math.ulp()*: return the value of the least significant bit of a float | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| `os <https://docs.python.org/3/whatsnew/3.9.html#os>`_ |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Exposed the Linux-specific *os.pidfd_open()* and *os.P_PIDFD* | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| The *os.unsetenv()* function is now also available on Windows | Complete |
+---------------------------------------------------------------------------------------------------------------+---------------+
| The *os.putenv()* and *os.unsetenv()* functions are now always available | Complete |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Added *os.waitstatus_to_exitcode()* function: convert a wait status to an exit code | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| `random <https://docs.python.org/3/whatsnew/3.9.html#random>`_ |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Added a new *random.Random.randbytes* method: generate random bytes | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| `sys <https://docs.python.org/3/whatsnew/3.9.html#sys>`_ |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Added a new *sys.platlibdir* attribute: name of the platform-specific library directory | |
+---------------------------------------------------------------------------------------------------------------+---------------+
| Previously, *sys.stderr* was block-buffered when non-interactive. Now stderr defaults to always being | |
| line-buffered | |
+---------------------------------------------------------------------------------------------------------------+---------------+
.. rubric:: Notes
.. [#pep584] PEP 584 ``dict`` union operator is only available on MicroPython builds with ``MICROPY_CPYTHON_COMPAT`` enabled.
|
