python3.8 new features

New features of python3.8

The stable version of Python3.8 has been released, and the official website has released an article introducing the new features Featured articles are recorded here.

New assignment operator:=

Function: Assign part of the value in a larger expression to a variable, because it seems Like the eyes and teeth of a walrus, the := operator has a special name: Walrus Operator

Example 1:

if (n := len(a)) > 10:    print(f"List is too long ({n} elements, expected <= 10)")

Use := to avoid calling len() twice.

New (positional parameters only) syntax symbols /

Function: Indicates that the parameters of some functions must specify positions and cannot be used as keyword parameters.

Example

def f(a, b, /, c, d, *, e, f):    print(a, b, c, d, e, f)

In this example, parameters a and b are positional parameters only, while c or d can be positional parameters only or keyword parameters, e and f must be a keyword argument.

New PYTHONPYCACHEPREFIX setting (-X pycache_prefix)

Function: configure the implicit bytecode cache to use a separate parallel file system tree instead of in Use the default pycache subdirectory in each source directory.

Debug builds share ABI with release builds

f New support for string = specifier for self-documenting expressions and debugging

f string is a formatted string literal, which was introduced in Python 3.6 and has become very popular.

This time, support for the = specifier is added in v3.8.

>>> user = 'eric_idle'>>> member_since = date(1975, 7, 31)>>> f'{user=} {member_since=}'"user='eric_idle' member_since=datetime.date(1975, 7, 31)"
>>> delta = date.today() - member_since>>> f'{user=!s}  {delta.days=:,d}''user=eric_idle  delta.days=16,075'

PEP 578: Python Runtime Audit Hooks / Runtime Audit Hooks

PEP adds audit hooks and verification open hooks. Both versions are available in Python and native code, allowing applications and frameworks written in pure Python code to take advantage of the additional notifications, while also allowing embedders or system administrators to always enable auditing. Deploy the Python build below.

PEP 587: Python Initialization Configuration

PEP 587 adds a new C API to configure Python initialization, providing better control over the entire configuration and better error report.

Others

continue finally can legally appear in the finally: block;

In Windows, the default asynchronous (asyncio) event loop has been changed to ProactorEventLoop

On macOS, the spawn start method is added to multiprocessing by default

Now multiprocessing can use shared memory segments to avoid pickle overhead between processes;

typed_ast is Merged back into CPython;

LOAD_GLOBAL is now 40% faster;

pickle now uses protocol 4 by default, improving performance;

numerouspython training videos, all on the Python Learning Network, welcome to online learning!

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