Walrus operator is the coolest feature that was added in the Python 3.8 update python codes.

start = input("Do you want to start(y/n)?")
print(start == "y")


# double parentheses here 
# using parentheses with the walrus operator is encouraged
print((start := input("Do you want to start(y/n)?")) == "y")

# With parentheses
if (sum := 10 + 5) > 10:
    print(sum) #return 15 
    
# Without parentheses 
if sum := 10 + 5 > 10:
    print(sum) #return True

a = [1, 2, 3, 4]
if (n := len(a)) > 3:
    print(f"List is too long ({n} elements, expected <= 3)")

2. Positional-only parameters

There is a new function parameter syntax / to indicate that some function parameters must be specified positionally and cannot be used as keyword arguments.

def name(positional_only_parameters, /, positional_or_keyword_parameters, *, keyword_only_parameters):

>>> def f(a,b,/,**kwargs):
...   print(a,b,kwargs)
...
>>> f(10,20,a=1,b=2,c=3)
10 20 {'a': 1, 'b': 2, 'c': 3}

def do_nothing(a, b, /):
  print(a, b)

>>> do_nothing(1, 2)
1, 2

>>> do_nothing(a=1, b=2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: do_nothing() takes no keyword arguments

1. mypy

Mypy is an optional static type checker for Python.

from typing import Union, Any, List, Optional, NoReturn, Dict, Tuple, Annotated, AnyStr

def fib(n: int) -> Iterator[int]:
    a, b = 0, 1
    while a < n:
        yield a
        a, b = b, a + b

Repo here.

Mypy supports reading configuration settings from a file.

# Global options:

[mypy]
python_version = 3.9
warn_return_any = True
warn_unused_configs = True

# Per-module options:

[mypy-mycode.foo.*]
disallow_untyped_defs = True

[mypy-mycode.bar]
warn_return_any = False

[mypy-somelibrary]
ignore_missing_imports = True

More configs here.

2. pylint

Pylint is a tool that checks for errors in Python code, tries to enforce a coding standard and looks for code smells. The default coding style used by Pylint is close to PEP 8. You can change config file to apply Google Style.

[MASTER]

# Specify a configuration file.
#rcfile=

# Python code to execute, usually for sys.path manipulation such as
# pygtk.require().
#init-hook=

# Files or directories to be skipped. They should be base names, not
# paths.
ignore=CVS

# Pickle collected data for later comparisons.
persistent=yes

pylintrc sample here.

docs here.

def name_of_function():
  '''
  python function name should be snake chasing
  '''

Arbitary arguments *args **kwargs

def func(*args):
  '''
  will get a tuple
  '''
  print(args)

def func(**kwargs):
  '''
  will get a dictionary
  '''
  if 'fruit' in kwargs:
    print(f"choice is {kwargs['fruit']}")
    
func(fruit='apple',veggie='lettuce')

2. yield

What does the “yield” keyword do?

the-python-yield-keyword-explained

def read_config(config):
    with open(config, 'r') as f:
        return list(map(lambda item: item.strip('\n'), f.readlines()))

2. How to get value from nested dictionary

def safe_get(dct, keys):
    for key in keys.split("."):
        try:
            dct = dct[key]
        except:
            return None
    return dct

3. How to rewrite the file

import json
with open (filename, 'r+') as json_file:
  	...
    json_file.seek(0,0)
    json.dump(data, json_file)

4. How to eliminate duplicate values in list

sth = list(set(sth))

5. How to create or remove dirs safely

import os, shutil

os.makedirs("temp", exist_ok=True)

if os.path.exists("temp") and os.path.isdir("temp"): shutil.rmtree("temp")

6. How to remove prefix

Python 3.9 or 3.9+

# 0. Remove prefix from the string
s0="abcPYTHONabc"
s0.removeprefix("abc")
#Output:PYTHONabc
s0.lstrip("abc")
#Output:PYTHONabc

# 1.The parameters of removeprefix() are considered as a substring. But parameters of lstrip() are considered as a set of characters
s1 = "abcbcacPYTHONabc"
s1.removeprefix("abc")
#Output:bcacPYTHONabc
s1.lstrip("abc")
#Output:PYTHONabc

# 2. removeprefix won't remove multiple copies of a prefix. But lstrip() will remove multiple copies of a prefix.
s2="abcabcPYTHONabc"
s2.lstrip("abc")
#Output:PYTHONabc
s2.removeprefix("abc")
#Output:abcPYTHONabc

# 3. If the parameter is not mentioned in lstrip(), it will remove leading whitespaces. But if the parameter is not mentioned in removeprefix(), it will raise TypeError.
s3="   PYTHON"
s3.lstrip()
#Output:PYTHON
s3.removeprefix()
#Output:TypeError: str.removeprefix() takes exactly one argument (0 given)

# 4. If the parameter mentioned is not found at the beginning of the string means, both methods will return a copy of the string.
s4="PYTHONabc"
s4.lstrip("abc")
#Output:PYTHONabc
s4.removeprefix("abc")
#Output:PYTHONabc

before Python 3.9

# 1. strip lstrip rstrip
str="abcbcxyyyyabcbc"
str.strip("abc")
#Output:xyyyy
str.lstrip("abc")
#Output:xyyyyabcbc
str.rstrip("abc")
#Output:abcbcxyyyy

# 2. re.sub()
import re
pattern_suffix=r"abc$"
pattern_prefix=r"^abc"
s="abcPYTHONacbcabc"
s_suffix=re.sub(pattern_suffix,"",s) #Output:abcPYTHONacbc
s_prefix=re.sub(pattern_prefix,"",s) #Output:PYTHONacbcabc

# 3. str.startswith()
s3="abcabcPythonacbcabc"
if (s3.startswith("abc")):
    print (s3.replace("abc","",1))
#Output:abcPythonacbcabc

Reference

remove prefix