Wissam Muneer

Wissam Muneer

1576865212

What’s New In Python 3.9

This article explains the new features in Python 3.9, compared to 3.8.

Note

Prerelease users should be aware that this document is currently in draft form. It will be updated substantially as Python 3.9 moves towards release, so it’s worth checking back even after reading earlier versions.

Summary – Release highlights

New Features

Other Language Changes

  • __import__() now raises ImportError instead of ValueError, which used to occur when a relative import went past its top-level package. (Contributed by Ngalim Siregar in bpo-37444.)

  • 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, sys.argv[0] and sys.path[0] become an absolute path, rather than a relative path. These paths now remain valid after the current directory is changed by os.chdir(). As a side effect, a traceback also displays the absolute path for __main__ module frames in this case. (Contributed by Victor Stinner in bpo-20443.)

  • In development mode and in debug build, encoding and errors arguments are now checked on string encoding and decoding operations. Examples: open(), str.encode() and bytes.decode().

  • 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. (Contributed by Victor Stinner in bpo-37388.)

  • "".replace("", s, n) now returns s instead of an empty string for all non-zero n. It is now consistent with "".replace("", s). There are similar changes for bytes and bytearray objects. (Contributed by Serhiy Storchaka in bpo-28029.)

New Modules

  • None yet.

Improved Modules

ast

Added the indent option to dump() which allows it to produce a multiline indented output. (Contributed by Serhiy Storchaka in bpo-37995.)

Added ast.unparse() as a function in the ast module that can be used to unparse an ast.AST object and produce a string with code that would produce an equivalent ast.AST object when parsed. (Contributed by Pablo Galindo and Batuhan Taskaya in bpo-38870.)

asyncio

Due to significant security concerns, the reuse_address parameter of asyncio.loop.create_datagram_endpoint() is no longer supported. This is because of the behavior of the socket option SO_REUSEADDR in UDP. For more details, see the documentation for loop.create_datagram_endpoint(). (Contributed by Kyle Stanley, Antoine Pitrou, and Yury Selivanov in bpo-37228.)

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()](https://docs.python.org/3.9/library/asyncio-task.html#asyncio.run "asyncio.run()") has been updated to use the new coroutine. (Contributed by Kyle Stanley in bpo-34037.)

Added asyncio.PidfdChildWatcher, a Linux-specific child watcher implementation that polls process file descriptors. (bpo-38692)

curses

Add curses.get_escdelay(), curses.set_escdelay(), curses.get_tabsize(), and curses.set_tabsize() functions. (Contributed by Anthony Sottile in bpo-38312.)

fcntl

Added constants F_OFD_GETLK, F_OFD_SETLK and F_OFD_SETLKW. (Contributed by Dong-hee Na in bpo-38602.)

os

Added CLD_KILLED and CLD_STOPPED for si_code. (Contributed by Dong-hee Na in bpo-38493.)

Exposed the Linux-specific os.pidfd_open() (bpo-38692) and os.P_PIDFD (bpo-38713) for process management with file descriptors.

threading

In a subinterpreter, spawning a daemon thread now raises a RuntimeError. Daemon threads were never supported in subinterpreters. Previously, the subinterpreter finalization crashed with a Python fatal error if a daemon thread was still running. (Contributed by Victor Stinner in bpo-37266.)

venv

The activation scripts provided by venv now all specify their prompt customization consistently by always using the value specified by __VENV_PROMPT__. Previously some scripts unconditionally used __VENV_PROMPT__, others only if it happened to be set (which was the default case), and one used __VENV_NAME__ instead. (Contributed by Brett Cannon in bpo-37663.)

pathlib

Added pathlib.Path.readlink() which acts similarly to os.readlink(). (Contributed by Girts Folkmanis in bpo-30618)

pprint

pprint can now pretty-print types.SimpleNamespace. (Contributed by Carl Bordum Hansen in bpo-37376.)

importlib

To improve consistency with import statements, importlib.util.resolve_name() now raises ImportError instead of ValueError for invalid relative import attempts. (Contributed by Ngalim Siregar in bpo-37444.)

signal

Exposed the Linux-specific signal.pidfd_send_signal() for sending to signals to a process using a file descriptor instead of a pid. (bpo-38712)

Optimizations

Build and C API Changes

  • Provide Py_EnterRecursiveCall() and Py_LeaveRecursiveCall() as regular functions for the limited API. Previously, there were defined as macros, but these macros didn’t work with the limited API which cannot access PyThreadState.recursion_depth field. Remove _Py_CheckRecursionLimit from the stable ABI. (Contributed by Victor Stinner in bpo-38644.)

  • Add a new public PyObject_CallNoArgs() function to the C API, which calls a callable Python object without any arguments. It is the most efficient way to call a callable Python object without any argument. (Contributed by Victor Stinner in bpo-37194.)

  • The global variable PyStructSequence_UnnamedField is now a constant and refers to a constant string. (Contributed by Serhiy Storchaka in bpo-38650.)

  • Exclude PyFPE_START_PROTECT() and PyFPE_END_PROTECT() macros of pyfpe.h from Py_LIMITED_API (stable API). (Contributed by Victor Stinner in bpo-38835.)

  • Remove PyMethod_ClearFreeList() and PyCFunction_ClearFreeList() functions: the free lists of bound method objects have been removed. (Contributed by Inada Naoki and Victor Stinner in bpo-37340.)

  • Remove PyUnicode_ClearFreeList() function: the Unicode free list has been removed in Python 3.3. (Contributed by Victor Stinner in bpo-38896.)

Deprecated

  • Currently math.factorial() accepts float instances with non-negative integer values (like 5.0). It raises a ValueError for non-integral and negative floats. It is now deprecated. In future Python versions it will raise a TypeError for all floats. (Contributed by Serhiy Storchaka in bpo-37315.)

  • The parser module is deprecated and will be removed in future versions of Python. For the majority of use cases, users can leverage the Abstract Syntax Tree (AST) generation and compilation stage, using the ast module.

  • The random module currently accepts any hashable type as a possible seed value. Unfortunately, some of those types are not guaranteed to have a deterministic hash value. After Python 3.9, the module will restrict its seeds to None, int, float, str, bytes, and bytearray.

  • Opening the GzipFile file for writing without specifying the mode argument is deprecated. In future Python versions it will always be opened for reading by default. Specify the mode argument for opening it for writing and silencing a warning. (Contributed by Serhiy Storchaka in bpo-28286.)

  • Deprecated the split() method of _tkinter.TkappType in favour of the splitlist() method which has more consistent and predicable behavior. (Contributed by Serhiy Storchaka in bpo-38371.)

Removed

  • array.array: tostring() and fromstring() methods have been removed. They were aliases to tobytes() and frombytes(), deprecated since Python 3.2. (Contributed by Victor Stinner in bpo-38916.)

  • The abstract base classes in collections.abc no longer are exposed in the regular collections module. This will help create a clearer distinction between the concrete classes and the abstract base classes.

  • The undocumented sys.callstats() function has been removed. Since Python 3.7, it was deprecated and always returned None. It required a special build option CALL_PROFILE which was already removed in Python 3.7. (Contributed by Victor Stinner in bpo-37414.)

  • The sys.getcheckinterval() and sys.setcheckinterval() functions have been removed. They were deprecated since Python 3.2. Use sys.getswitchinterval() and sys.setswitchinterval() instead. (Contributed by Victor Stinner in bpo-37392.)

  • The C function PyImport_Cleanup() has been removed. It was documented as: “Empty the module table. For internal use only.” (Contributed by Victor Stinner in bpo-36710.)

  • _dummy_thread and dummy_threading modules have been removed. These modules were deprecated since Python 3.7 which requires threading support. (Contributed by Victor Stinner in bpo-37312.)

  • aifc.openfp() alias to aifc.open(), sunau.openfp() alias to sunau.open(), and wave.openfp() alias to wave.open() have been removed. They were deprecated since Python 3.7. (Contributed by Victor Stinner in bpo-37320.)

  • The isAlive() method of threading.Thread has been removed. It was deprecated since Python 3.8. Use is_alive() instead. (Contributed by Dong-hee Na in bpo-37804.)

  • Methods getchildren() and getiterator() in the ElementTree module have been removed. They were deprecated in Python 3.2. Use functions list() and iter() instead. The xml.etree.cElementTree module has been removed. (Contributed by Serhiy Storchaka in bpo-36543.)

  • The old plistlib API has been removed, it was deprecated since Python 3.4. Use the load(), loads(), dump(), and dumps() functions. Additionally, the use_builtin_types parameter was removed, standard bytes objects are always used instead. (Contributed by Jon Janzen in bpo-36409.)

  • The C function PyThreadState_DeleteCurrent() has been removed. It was not documented. (Contributed by Joannah Nanjekye in bpo-37878.)

  • The C function PyGen_NeedsFinalizing has been removed. It was not documented, tested, or used anywhere within CPython after the implementation of PEP 442. Patch by Joannah Nanjekye. (Contributed by Joannah Nanjekye in bpo-15088)

Porting to Python 3.9

This section lists previously described changes and other bugfixes that may require changes to your code.

Changes in the Python API

  • open(), io.open(), codecs.open() and fileinput.FileInput no longer accept 'U' (“universal newline”) in the file mode. This flag was deprecated since Python 3.3. In Python 3, the “universal newline” is used by default when a file is open in text mode. The newline parameter of open() controls how universal newlines works. (Contributed by Victor Stinner in bpo-37330.)

  • import() and importlib.util.resolve_name() now raise ImportError where it previously raised ValueError. Callers catching the specific exception type and supporting both Python 3.9 and earlier versions will need to catch both using except (ImportError, ValueError):.

  • The venv activation scripts no longer special-case when __VENV_PROMPT__ is set to "".

CPython bytecode changes

Find More: https://docs.python.org/3/whatsnew/3.9.html

#python #web-development #machine-learning #programming #developer

What is GEEK

Buddha Community

What’s New In Python 3.9
Ray Patel

Ray Patel

1619518440

top 30 Python Tips and Tricks for Beginners

Welcome to my Blog , In this article, you are going to learn the top 10 python tips and tricks.

1) swap two numbers.

2) Reversing a string in Python.

3) Create a single string from all the elements in list.

4) Chaining Of Comparison Operators.

5) Print The File Path Of Imported Modules.

6) Return Multiple Values From Functions.

7) Find The Most Frequent Value In A List.

8) Check The Memory Usage Of An Object.

…

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Ray Patel

Ray Patel

1619510796

Lambda, Map, Filter functions in python

Welcome to my Blog, In this article, we will learn python lambda function, Map function, and filter function.

Lambda function in python: Lambda is a one line anonymous function and lambda takes any number of arguments but can only have one expression and python lambda syntax is

Syntax: x = lambda arguments : expression

Now i will show you some python lambda function examples:

#python #anonymous function python #filter function in python #lambda #lambda python 3 #map python #python filter #python filter lambda #python lambda #python lambda examples #python map

Ray Patel

Ray Patel

1623406860

What’s New in Python 3.10?

A rundown of the coolest features

Python 3.10 development has stabilized and we can finally test out all of the new features that will be included in the final release.

We’ll cover some of the most interesting additions to Python — structural pattern matching, parenthesized context managers, _more _typing, and the new and improved error messages.

Check out the video version of the article here:

Structural Pattern Matching

Parenthesized Context Managers

More Typing

…

#data-science #programming #programming-languages #python #what’s new in python 3.10 #python 3.10

Luna Hermann

Luna Hermann

1598897520

What Are The New Features in Python 3.9?

It’s that time again, a new version of Python is imminent. Now in beta (3.9.0b3), we will soon be seeing the full release of Python 3.9.

Some of the newest features are incredibly exciting, and it will be amazing to see them used after release. We’ll cover the following:

  • Dictionary Union Operators
  • Type Hinting
  • Two New String Methods
  • New Python Parser

— this is very cool

Let’s take a first look at these new features and how we use them.

Dictionary Unions

One of my favorite new features with a sleek syntax. If we have two dictionaries a and b that we need to merge, we now use the union operators.

We have the **merge **operator |:

a = {1: 'a', 2: 'b', 3: 'c'}
b = {4: 'd', 5: 'e'}
c = a | b
print(c)

[Out]: {1: ‘a’, 2: ‘b’, 3: ‘c’, 4: ‘d’, 5: ‘e’}

And the **update **operator |=, which updates the original dictionary:

a = {1: 'a', 2: 'b', 3: 'c'}
b = {4: 'd', 5: 'e'}
a |= b
print(a)

[Out]: {1: ‘a’, 2: ‘b’, 3: ‘c’, 4: ‘d’, 5: ‘e’}

If our dictionaries share a common key, the key-value pair in the second dictionary will be used:

a = {1: 'a', 2: 'b', 3: 'c', 6: 'in both'}
b = {4: 'd', 5: 'e', 6: 'but different'}
print(a | b)

**[Out]: **{1: ‘a’, 2: ‘b’, 3: ‘c’, 6: ‘but different’, 4: ‘d’, 5: ‘e’}

Dictionary Update with Iterables

Another cool behavior of the |= operator is the ability to **update **the dictionary with new key-value pairs using an iterable object — like a list or generator:

a = {'a': 'one', 'b': 'two'}
b = ((i, i**2) for i in range(3))
a |= b
print(a)

#python #python-programming #latest-tech-stories #python-top-story #python3 #learn-python #programming #python-tips

Biju Augustian

Biju Augustian

1574340704

The Python 3 New Features from Python Enhancement Proposal

Description
Python 2 will end of life in 2020!!!

If you are a Python 2 developer, it’s time to porting your code into Python 3 !!!

Course Summary

If you are a Python 2 developer and haven’t had the chance to use Python 3, this course is for you. We will talk about Python 3 new feature with demos and make sure you can understand them all
What’s this course about and why you should take it?

This course let you master the new and cool features in Python 3
We assume you have a base knowledge of the subset of Python that runs in Python 2 and 3. We dive deep into every aspect of Python 3 and the PEP’s that prompted those changes. From advanced string formatting, number updates, changes in classes and functions, to Unicode, Type annotation and synchronous Programming, this course covers it all. You will see the features in action and try them out for yourself
Who is this course for?

For anyone who has wanted to dive into the new features of Python 3. It is quite easy to write code that works in both Python 2 and 3. Many old Python developers are used to the features of 2 and have never looked into all of the new features that Python 3 provides. Many new programmers are using Python 3, but are missing out on new features like async and annotations
Existing Python 3 users: If you aren’t using Python to its full potential, you owe it to yourself to checkout this course and see a wealth of Python 3 features that you might not even know exist. You will see and explore most of them in this course!
Basic knowledge
Requirements

Beginner level of python 2 programmer
A computer installed Python 3
What will you learn
understand the differences between Python 2 and Python 3
can port their own code from python 2 to python 3
write python 3 native code
learn Python 3 new feature

# Python 3 #Python Enhancement Proposal # Python 3 New Features from Python Enhancement Proposal