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 and a detailed description of the changes can be found in What’s New in Python 3.9
Features |
Status |
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Fast access to module state from methods of C extension types |
Not relevant |
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Union operators added to dict |
Complete [1] |
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Type hinting generics in standard collections |
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Flexible function and variable annotations |
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CPython adopts an annual release cycle. Instead of annual, aiming for two month release cycle |
Not relevant |
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Relaxed grammar restrictions on decorators |
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The IANA Time Zone Database is now present in the standard library in the zoneinfo module |
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String methods to remove prefixes and suffixes |
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CPython now uses a new parser based on PEG |
Not relevant |
Other Language Changes:
__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 |
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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 |
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“”.replace(“”, s, n) now returns s instead of an empty string for all non-zero n. It is now consistent with “”.replace(“”, s) |
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Any valid expression can now be used as a decorator. Previously, the grammar was much more restrictive |
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Parallel running of aclose() / asend() / athrow() is now prohibited, and ag_running now reflects the actual running status of the async generator |
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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 |
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Unparenthesized lambda expressions can no longer be the expression part in an if clause in comprehensions and generator expressions |
Changes to built-in modules:
Due to significant security concerns, the reuse_address parameter of asyncio.loop.create_datagram_endpoint() is no longer supported |
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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. |
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Added asyncio.PidfdChildWatcher, a Linux-specific child watcher implementation that polls process file descriptors |
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added a new coroutine asyncio.to_thread() |
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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 |
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asyncio now raises TyperError when calling incompatible methods with an ssl.SSLSocket socket |
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Garbage collection does not block on resurrected objects |
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Added a new function gc.is_finalized() to check if an object has been finalized by the garbage collector |
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Expanded the math.gcd() function to handle multiple arguments. Formerly, it only supported two arguments |
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Added math.lcm(): return the least common multiple of specified arguments |
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Added math.nextafter(): return the next floating-point value after x towards y |
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Added math.ulp(): return the value of the least significant bit of a float |
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Exposed the Linux-specific os.pidfd_open() and os.P_PIDFD |
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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 |
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Added a new random.Random.randbytes method: generate random bytes |
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Added a new sys.platlibdir attribute: name of the platform-specific library directory |
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Previously, sys.stderr was block-buffered when non-interactive. Now stderr defaults to always being line-buffered |
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Notes