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What’s New in Python 3.9 alpha2?

abdurrahmaanj profile image Abdur-Rahmaan Janhangeer Originally published at pythonmembers.club ・2 min read

Python is set to release a new version next year, the shiny 3.9. This one omitted the sys.argv change rolled back in alpha2 Here’s our take of the most noticeable changes:

Keyword Arguments Get Some Boost

improved

sebastian@seberg-x1 ~/python-dev/bin
 % ./python3 -m timeit -s 'i = 4' 'i.to_bytes(length=5, byteorder="big", signed=True)'
1000000 loops, best of 5: 205 nsec per loop
sebastian@seberg-x1 ~/python-dev/bin
 % ./python3 -m timeit -s 'i = 4' 'i.to_bytes(length=5, byteorder="big", signed=True)'
1000000 loops, best of 5: 207 nsec per loop

original

sebastian@seberg-x1 ~/python-dev/bin
 % ./python3 -m timeit -s 'i = 4' 'i.to_bytes(length=5, byteorder="big", signed=True)'
1000000 loops, best of 5: 221 nsec per loop
sebastian@seberg-x1 ~/python-dev/bin
 % ./python3 -m timeit -s 'i = 4' 'i.to_bytes(length=5, byteorder="big", signed=True)'
1000000 loops, best of 5: 218 nsec per loop

Audit hooks added for sys.excepthook() and sys.unraisablehook()

Audit hooks were added in PEP 578. It basically allows you to monitor low-level details. It’s aim is to monitor behaviors of Python scripts more accurately. Example of use in the wording of the PEP:

Auditing bypass can occur when the typical system tool used for an action would ordinarily report its use, but accessing the APIs via Python do not trigger this. For example, invoking “curl” to make HTTP requests may be specifically monitored in an audited system, but Python’s “urlretrieve” function is not.

Calling replace on a code object now raises the code.new audit event.
The code object is returned when using the in-built compile() function on some codes. The corresponding C code:

   if (PySys_Audit("code.__new__", "OOOiiiiii",
                    co_code, co_filename, co_name, co_argcount,
                    co_posonlyargcount, co_kwonlyargcount, co_nlocals,
                    co_stacksize, co_flags) < 0) {
        return NULL;
    }

Thread stack size set to 8 Mb for debug builds on Android

An initiated script crashes on Android API 24 but only in debug mode. The maximum recursion limit was reduced from 1000 to 100.

In Python you can’t recurse more than some limit.

>>> import sys
>>> sys.getrecursionlimit()
1000

The above patch was implemented by defining THREAD_STACK_SIZE to 8mb

define THREAD_STACK_SIZE    0x800000

Added __floor__ and __ceil__ method to float object

Was not previously implemented. Also added tests.

Use of python -m pip instead of pip to upgrade dependencies in venv

In cpython/Lib/venv/init.py alongsize some other changes, the below update sets python -m pip install as default for dependencies upgrade

        if sys.platform == 'win32':
            python_exe = os.path.join(context.bin_path, 'python.exe')
        else:
            python_exe = os.path.join(context.bin_path, 'python')
        cmd = [python_exe, '-m', 'pip', 'install', '--upgrade']
        cmd.extend(CORE_VENV_DEPS)
        subprocess.check_call(cmd)

Excape key also closes IDLE completion windows

Many keys are used in auto completion. The escape key was just added

KEYPRESS_SEQUENCES = ("<Key>", "<Key-BackSpace>", "<Key-Return>", "<Key-Tab>",
                      "<Key-Up>", "<Key-Down>", "<Key-Home>", "<Key-End>",
                      "<Key-Prior>", "<Key-Next>", "<Key-Escape>")

That’s was my funnified personal pick!

An original PythonMembersClub pub.

Discussion (1)

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wrldwzrd89 profile image
Eric Ahnell

What I'm curious about is if 3.9 fixes the last of the post-3.3 performance regressions in 3.4+. Python 3.7 improved a ton of these, and 3.8 fixes all but a few. Thanks for the list!

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