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Python

Access attribute using string​

getattr(object, name, default=None)
hasattr(object, name)

pip - PIP Installs Packages​

Reference

CLI

pip
python -m pip

Install package

pip install <package>

Uninstall package

pip uninstall <package>

List installed package

pip list

Download package

pip download <package>

Install downloaded package

pip install --no-index --find-links <directory> <package>

Export requirements.txt

pip freeze > requirements.txt

Install requirements.txt

pip install -r requirements.txt

Download requirements.txt

pip download -r requirements.txt

Formatter​

Unit test​

pytest reference / Reference

module/
    lib/
        __init__.py
        module.py
    tests/
        test_module.py
# test_module.py

import unittest
from lib import module

class TestModule(unittest.TestCase):
    def test_module(self):
        pass

if __name__ == '__main__':
    unittest.main()
# In /module/ folder
python -m tests.test_module

Unit test framework​

Show sys.path (module path) in CLI​

python -m site

Pass all arguments to another function​

class List(list):
    def append_twice(self, *args, **kwargs):
        self.append(*args, **kwargs)
        self.append(*args, **kwargs)

Decorator​

Reference

@decorator
def run():
    pass

is equivalent to

def run():
    pass
run = decorator(run)
from functools import wraps

def decorator(func):
    # Using original func name and doc string
    @wraps(func)
    def wrap():
        print("[Before]")
        func()
        print("[After]")
    return wrap

@decorator
def run():
    print("Run")

run()

# [Before]
# Run
# [After]

Bind self to function​

Reference

import types

def power(self, exp):
    return pow(self, exp)

power2 = types.MethodType(power, 2)
print(power2(8)) # 256

Follow file​

Follow file changed / appended data

from io import SEEK_CUR, SEEK_END, SEEK_SET
from typing import Iterator, TextIO
import sys


def follow(file: TextIO, interval: float = 0.2) -> Iterator[str]:
    from time import sleep
    line = ''
    while True:
        new = file.readline()
        if new == "":
            sleep(interval)
            continue
        line += new
        if not line.endswith("\n"):
            continue
        yield line[:-1]
        line = ''


if __name__ == '__main__':
    with open("access.log", 'r') as file:
        file.seek(0, SEEK_END)
        for line in follow(file):
            print(line)

Is iterable ?​

from collections.abc import Iterable

isinstance(e, Iterable):