python_cheat_sheet.md

Python Cheat Sheet

Dependency in Python

• virtualenv venv -p /usr/local/bin/python3
• source ./venv/bin/activate
• pip freeze > requirements.txt
• pip install -r requirements.txt

Check for None (Null)

Use foo is None instead foo == None

Mutable

• check memory ```id(foo)``
• foo.append(1) —> mutable (id same)
• foo = 1 —> immutable (id changed)

Execute a Python Script

add on first line: #! /usr/bin/env python

Format String

• Multiline

multiline= """Will's ball
... is red
... and bouncy!"""

• Format string:

print("Will's %s is %s." % (item, color))

• Format with .format

print("Will's {0} is {1}".format(item, color))

Python Method

• See available method with dir()
• method help with help("will".rstrip)

Flow Control

• if (condition):
  • elif (condition):
  • else:
• for i in range(5):
• range(min, max, increase/decrese)
  • range(10, 0, -1)

Comparison Operators

• ==, !=, >, <. <=, >=
• and, or, is, in

Lists

• [] ex: [1, 'cat', 7, {'car': 'chevy'}]
• [].append(element)
• [].remove(element)
• [].pop(index = element.count() -1)
• [].sort()
• [].reverse()
• [].count()
• slice with [][fromIndex:position]

a = [1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> a[2:5]
[3, 4, 5]

>>> a[2:]
[3, 4, 5, 6, 7, 8, 9]
>>> a[:5]
[1, 2, 3, 4, 5]
>>> a[-4:]
[6, 7, 8, 9]

>>> a[2:5] = ['foo', 'bar', 'baz']
>>> a
[1, 2, 'foo', 'bar', 'baz', 6, 7, 8, 9]

>>> zoo_animals = ['giraffe', 'monkey', 'elephant', 'lion', 'bear', 'pig', 'horse', 'aardvark']
>>> my_animals = ['monkey', 'bear', 'pig']

>>> not_my_animals = []
>>> for animal in zoo_animals:
...     if animal not in my_animals:
...             not_my_animals.append(animal)
... 
>>> not_my_animals
['giraffe', 'elephant', 'lion', 'horse', 'aardvark']

>>> other_animals = [animal for animal in zoo_animals if animal not in my_animals]
>>> other_animals
['giraffe', 'elephant', 'lion', 'horse', 'aardvark']

Manipulate Data with Dictionaries

• key in {}
• del dict[‘key’]
• get value: dict.get(‘key1’, ‘default value’)

Immutable Data with Tupple

• t = 'dog', 'cat', 12345

Unique Unordered Collections with Set

• animals = {'monkey', 'bear', 'dog', 'monkey', 'cat', 'bear', 'gorilla'}
• fish = set()
• add, remove, pop, in, union

Logging in Python

• import logging
• logging.warning
• critical, error, warning, info, debug
• logging.basicConfig(filename='./demo.log', level=logging.INFO