python.md

Ternary operator

x = 1 if condition else 0

Large numbers

num = 10000000000

• is same as:

num = 10_000_000_000

• and to print it with commas:

print(f'{num:,}')

Context manager

{% hint style="info" %} When managing resources (files, database, streams) consider using context manager {% endhint %}

with open('test.txt', 'r') as f:
  file_contents = f.read()

words = file_contents.split(' ')
word_count = len(words)
print(word_count)

Access index in for loop

arr = ['one', 'two', 'three']

for index, num in enumerate(arr, start = 0):
  print(index, num)

Loop through 2 or more arrays

names = ['Peter Parker', 'Bruce Wayne', 'Barry Allen']
heroes = ['Spiderman', 'Batman', 'Flash']

for name, hero in zip(names, heroes):
  print(f'{name} is {hero}')

Unpacking

a, b = (1, 2)
a, _ = (1, 2) # if second var is not used
a, b, *c = (1, 2, 3, 4, 5) # c is everthing else in array
a, b, *_ = (1, 2, 3, 4, 5)
a, b, *c, d = (1, 2, 3, 4, 5)

Class attributes access

class Person():
  pass

person = Person()

first_key = 'first'
first_val = 'Alex'

setattr(person, first_key, first_val)

first = getattr(person, first_key)

Hide password or input

from getpass import getpass

username = input('username')
password = getpass('password')

virtualenv

• mkdir project
• python3 -m venv project/venv --upgrade-deps
• source project/venv/bin/activate
• python3 -m pip install -U autopep8
• pip freeze > requirements.txt
• pip install -r requirements.txt
• deactivate

Save dependencies to requirements

pip freeze --local requirements.txt

Specify version of python

virtualenv -p /usr/bin/python2.6 py2_project

Flask

Basic app

from flask import Flask
app = Flask(__main__)


@app.route("/")
def hello():
    return "hello"

export FLASK_APP=main.py
flask run

Turn on debug mode

export FLASK_DEBUG=1