Python 3.9
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 | |
|---|---|---|
| PEP 573 | Fast access to module state from methods of C extension types | Not relevant |
| PEP 584 | Union operators added to dict | Complete |
| PEP 585 | Type hinting generics in standard collections | |
| PEP 593 | Flexible function and variable annotations | |
| PEP 602 | CPython adopts an annual release cycle. Instead of annual, aiming for two month release cycle | Not relevant |
| PEP 614 | Relaxed grammar restrictions on decorators | |
| PEP 615 | The IANA Time Zone Database is now present in the standard library in the zoneinfo module | |
| PEP 616 | String methods to remove prefixes and suffixes | |
| PEP 617 | 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 | |
| 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:
| 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 | |
| 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 | |
| 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 | |
| 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 | |
| Added a new random.Random.randbytes method: generate random bytes | |
| 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 |
Notes
PEP 584 dict union operator is only available on MicroPython builds with MICROPY_CPYTHON_COMPAT enabled.