Python cheatsheet

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Basics

ABC Basics

name = input() # gets input from a user
len("Hello") # prints a string length
str(20) # converts number to string
int("20") # converts string to number
float("20.5") # converts string to float
round(33.33333, 2) # round a number to two decimal places
bool("true") # string to boolean

None datatype is equal to null in Java.

Import

#!/us/bin/python

import gi # import a package
from games import NumberGuessing # import a class from 'games' package

Multi Import

import random, sys, os, math

Different Import approaches

import random

random.randint(1, 20)

from random import *

randin(1, 200)

Print

text = "Hello World!"

print(text*2) # print 'Hello World!' twice

# add space automatically 

name = "Mike"
print("Hello", name, "How are you?") # print Hello Mike How are you?

String interpolation

value = 4 * 20

print("The value is {value}".format(value=value)) # print 'The value is 80' 

# without specifying the parameter name explicitly

print("The value is {value}".format(value)) # print 'The value is 80'

# passing parameters in order

text = "Hello {0}. Are you really {1} years old?"

print(text.format("Mike", 30)) # print 'Hello Mike. Are you really 30 years old?'

# passing parameters via a dictionary

a_dict = {
    "firstName": "Mike",
    "lastName": "Miller",
    "age": "30"
}

a_str = "Hello {firstName} {lastName}. Your age is {age}"

print(a_str.format(**a_dict)) # print 'Hello Mike Miller. Your age is 30'

String manipulation

st = '''
Here goes
multiple line
of a string
'''

print(r 'John\'s house') # raw prints John\'s house instead of John's house

# Multiline comment
"""
Some comments
to add here
"""

hello_str = "Hello World"

hello_str[0:5] # sub string, returns 'Hello'

"Hello" in hello_str # search in a string, returns true
hello_str.upper() # to uppercase
hello_str.lower() # to lowercase
hello_str.isupper() # check whether a string is in uppercase
hello_str.islower() # check whether a string is in lowercase
hello_str.isalpha() # whether a string is all alphabet and is not blank
hello_str.isalnum() # whether a string is alphanumeric and is not blank
hello_str.isdecimal() # whether a string is only consists of number and is not blank
hello_str.isspace() # whether a string only consists of whitespaces
hello_str.istitle() # whether a string has first character of each word in uppercase like 'Hello World'
hello_str.startswith("Hello") # whether a string starts with a certain substring
hello_str.endswith("World") # whether a string ends with a certain substring
hello_str.split() # split a string to a list base on space ['Hello', 'World'], also can pass separator as argument .split("\t")
", ".join(['Hello', 'World']) # converts a list to a string and use ',' as delimiter
hello_str.strip() # removes all whitespaces from left and right sides of a string
hello_str.lstrip() # removes all whitespaces from left side of a string
hello_str.rstrip() # removes all whitespaces from right side of a string

# clipboard 
import pyperclip
pyperclip.copy('Hello world!')
pyperclip.paste()

Pattern matching

import re
regex = re.compile(r'\d\d\d-\d\d\d-\d\d\d\d') # match number in 123-456-7890 format
m = regex.search('My number is 123-567-4242.')
print(m.group()) # prints 123-567-4242
re.compile(r'(\d\d\d)-(\d\d\d-\d\d\d\d)') # separating area code
m = regex.search('My number is 123-567-4242.')
print(m.group(1)) # 123
print(m.group(2)) # 567-4242
print(m.group()) # 123-567-4242
regex = re.compile(r'(\(\d\d\d\)) (\d\d\d-\d\d\d\d)') # parentheses support
m = regex.search('My number is (021) 123-4567')
print(m.group(1)) # (021)
print(m.group(2)) # 123-4567
print(m.group()) # (021) 123-4567
regex = re.compile(r'John|Jacob') # either or matches the first only
m = regex.search('John and Jacob are friends')
print(m.group()) # John
lst = regex.findall('John and Jacob are friends') # find all occurrences
print(lst) # ['John', 'Jacob']
regex = re.compile(r'John (Wick|Anderson|Smith)') # match first should be John and (Wick or Anderson or Smith)
m = regex.search('Johns are friends, especially John Wick and John Smith')
print(m.group) # prints John wick
batRegex = re.compile(r'Bat(wo)?man') # optional either should match Batman or Batwoman `(wo)?` indicates `wo` is optional
m = batRegex.search('The Adventures of Batman')
print(m.group()) # prints Batman

batRegex = re.compile(r'Bat(wo)*man') # optional either should match Batman or Batwoman or Batwowowoman `(wo)*` 
# indicates either zero or more instance `wo` is matching
m = batRegex.search('The Adventures of Batman')
print(m.group()) # prints Batman
m = batRegex.search('The Adventures of Batwoman')
print(m.group()) # prints Batwoman
m = batRegex.search('The Adventures of Batwowoman')
print(m.group()) # prints Batwowoman
m = batRegex.search('The Adventures of Batwowowoman')
print(m.group()) # prints Batwowowoman

batRegex = re.compile(r'Bat(wo)+man') # optional either should match Batwoman or Batwowowoman `(wo)+` 
# but no Batman. Indicates at least one instance `wo` is matching
m = batRegex.search('The Adventures of Batman') # matches nothing
m = batRegex.search('The Adventures of Batwoman')
print(m.group()) # prints Batwoman
m = batRegex.search('The Adventures of Batwowoman')
print(m.group()) # prints Batwowoman
m = batRegex.search('The Adventures of Batwowowoman')
print(m.group()) # prints Batwowowoman

regex = re.compile(r'(Ha){3}') # repetition match, indicates `Ha` strings repeated EXACTLY three times
m = regex.search('HaHa') # matches nothing
m = regex.search('HaHaHa')
print(m.group()) # prints HaHaHa
m = regex.search('HaHaHaHa') # matches nothing

regex = re.compile(r'(Ha){3,5}') # repetition match, indicates `Ha` string repeated between three to five times
m = regex.search('HaHa') # matches nothing
m = regex.search('HaHaHa')
print(m.group()) # prints HaHaHa
m = regex.search('HaHaHaHa')
print(m.group()) # prints HaHaHaHa which is greedy
# none greedy
regex = re.compile(r'(Ha){3,5}?')
m = regex.search('HaHaHaHa')
print(m.group()) # prints HaHaHa which is none greedy

# character classes
# \d Any numeric digit from 0 to 9
# \D Any character that is not a numeric digit from 0 to 9 
# \w Any letter, numeric digit, or the underscore character (word)
# \W Any character that is not a letter, numeric digit, or the underscore character
# \s Any space, tab, or newline character. (Think of this as matching “space” characters.)
# \S Any character that is not a space, tab, or newline.

# custom character class
regex = re.compile(r'[2468]') # match only odd number
m = regex.findall('12 3456 7890') # matches ['2', '4', '6', '8']

regex = re.compile(r'[^02468]') # not condition which essentially matches odd numbers and any other characters like space

regex = re.compile(r'^hello') # means hello should be at the begining
m = regex.search('hello world') # returns hello
m = regex.search('world! hello') # returns nothing
regex = re.compile(r'hello$') # means hello should be at the end
m = regex.search('hello world') # returns nothing
m = regex.search('world! hello') # returns hello

atRegex = re.compile(r'.at') # matches anything at has at in it
atRegex.findall('The cat in the hat sat on the flat mat.') # returns ['cat', 'hat', 'sat', 'lat', 'mat']

nameRegex = re.compile(r'First Name: (.*) Last Name: (.*)') # match anything started with First Name: and then anything 
# and then followed by Last Name: anything
m = nameRegex.search('First Name: Al Last Name: Sweigart')
print(m.group(0)) # prints Al
print(m.group(1)) # prints Sweigart

noNewlineRegex = re.compile('.*') # newline match

regex = re.compile(r'hello', re.I) # ignore case

namesRegex = re.compile(r'Agent \w+') # string substitution
namesRegex.sub('CENSORED', 'Agent Alice gave the secret documents to Agent Bob.') # 'CENSORED gave the secret documents to CENSORED.'

List

lst = ["One", "Two", "Three", "Four", "Five"]

# print a list elements one by one
for element in lst:
    print(element)
    
print(len(lst)) # list length

print(lst[2]) # get third element of a list

lst_copy = lst.copy() # copy python 3

lst_copy = lst[:] # copy list for both python 2 and 3

lst[1:] # ['Two', 'Three', 'Four', 'Five']
lst[:2] # ['One', 'Two']
lst[-2:] # ['Four', 'Five']
lst[:-2] # ['One', 'Two', 'Three']
lst[-1] # 'Five'

lst.append("Six") # append a new element to a list

two = lst.pop(1) # get and remove "Two" from the list

lst.pop(0) # removes element "One" from the list

lst = ['Hello', 'Hallo', 'Howdy']
lst1 = ['A', 'B', 'C']
del lst[0] # remove 'Hello'
lst.remove('Howdy')
new_lst = lst + lst1 # concat list
lst = lst + "XXX"
'Howdy' in lst # search for an element in list
lst1.sort() # sort a list
import copy
lst_copy = copy.copy(lst) # create a copy with different reference
lst_copy_deep = copy.deepcopy(lst) # create a deep copy which supports inner lists and objects with different references

Dictionary

a_dict = {
    1: "One",
    2: "Two",
    3: "Three",
    4: "Four",
    5: "Five"
}

a_dict[2] # return 'two'

a_dict[6] # throw exception

a_dict.get(6) # return None 

a_dict[6] = "Six" # append to dictionary

a_dict[1] = "Something else" # change the value of key '1'

a_dict+={10: "Ten"}

print(a_dict[5] * 2) # print 'FiveFive'

len(a_dict) # get dictionary length

# iterating through a dictionary
for i in a_dict.keys():
    print("{key} = {value}".format(key = i, value = a_dict[i]))


# filtering string in a dictionary and modifying it at the same time
str_lst = []

for element in a_dict.copy().keys():
    if isinstance(element, str):
        a_dict.pop(element)
        str_lst.append(element)

keys(), values(), items(), get(), setdefault() in a dictionary

d = { "first_name": "John", "last_name": "Wick", "age": 44}

d.keys() # return first_name, last_name, age
d.values() # return John, Wick, 44
d.items() # return a dict_items of tuple ([('first_name', 'John'), ('last_name', 'Wick'), ('age', 44)])
d.get("first_name") # return John
d.setdefault("first_name", "David") # tries to get the value of first_name key, if doesn't exist set the default

Conditions


x = 10

if x is 10:
    print("Ten")
elif x == 9:
    print("Nine")
else:
    print("Unknown")

text = "Hello world!"

if isinstance(text, str):
    print("It's a text message")
elif isinstance(text, int):
    print("It's an integer")
else:
    print("Noops")

number = 3

if number > 0 and number % 2 is not 0:
    print("Something")
elif number > 0 or number == 3:
    print("Something else")

Loop


lst = ["One", "Two", "Three", "Four", "Five"]

# for-each type of loop
for element in lst:
    print(element)

# traditional for-loop
for i in range(len(lst)):
    print(lst[i])
    
for i in range(10, 20):
    print(i) # print 10 to 19 NOT 20

# while-loop
i, n = 0, 20 
while i < n:
    print(i) # print 0 to 19
    i += 1

Class


# class creation
class Person:
    __age = 0 # similar to private field

    __gender = "Male" # similar to private field

    def get_age(self):
        return self.__age

    def get_gender(self):
        return self.__gender
        
    def set_gender(self, gender = "Male"):
        self.__gender = gender     

# class instantiation

a_person = Person()

print(a_person.get_gender())

a_person.set_gender("Female")

print(a_person.get_gender())

a_person.set_gender()

print(a_person.get_gender())

Inheritance

class Mammal:

    __name = "Nothing"

    __age = 0

    __gender = "Male"

    def __init__(self, name):
        self.__name = name

    def get_name(self):
        return self.__name

    def get_age(self):
        return self.__age

    def set_age(self, age):
        self.__age =  age

    def get_gender(self):
        return self.__gender

    def set_gender(self, gender):
        self.__gender = gender


class Human(Mammal):

    __education = "Diploma"

    __occupation = "Developer"

    def __init__(self, age, gender, education, occupation):
        # calling parent class method
        super().__init__("Human")
        super().set_age(age)
        super().set_gender(gender)
        self.__education = education
        self.__occupation = occupation

    def get_education(self):
        return self.__education

    def get_occupation(self):
        return self.__occupation


cat = Mammal("Kitty")
cat.set_age(2)
cat.set_gender("Female")
print(cat.get_age())

developer = Human(30, "Male", "Masters", "Developer")
print(developer.get_age())

Abstract Base Class (ABC) or Interface

# Base class
import abc


class Game(metaclass=abc.ABCMeta):

    @abc.abstractmethod
    def get_name(self):
        pass

    @abc.abstractmethod
    def play(self):
        pass

# Implementation


import random

from games import Game


class NumberGuessing(Game):
    def get_name(self):
        # method implementation

    def play(self):
        # method implementation

Get and initialize subclasses of a class


# Defining parent and child classes
class Parent:
    
    def printHello(self):
        print("Hello")
        
class ChildOne(Parent):
    
    def printHello(self):
        print("Hallo")

class ChildTwo(Parent):
    
    def printHello(self):
        print("Hola!")

children = [cls() for cls in Parent.__subclasses__()]


for child in children:
    child.printHello() # prints 'Hallo' and 'Hola!'

Get type and type comparison

tup = (1, 2, 3, 4)
type(tup) # prints <class 'tuple'>
isinstance(tup, tuple) # prints 'True'
isinstance(tup, dict) # prints 'False'
isinstance(tup, list) # prints 'False'

Interaction with pip

$ pip install [package name] # install system-wide
$ pip install [package name] --user # install per user
$ pip uninstall [package name] # remove a package

Working with files

OS path

import os
os.path.join("home", "John", "Desktop") # returns a joined path of /home/John/Desktop
os.getcwd() # get current directy
os.chdir("/usr/bin") # change directory
os.path.basename("/home/john/notes.txt") # gets filename `notes.txt`
os.path.dirname("/home/john/notes.txt") # gets path excluding the filename `/home/john`
os.path.split("/home/john/notes.txt") # splits the path to a list of [filename, file path]
os.path.getsize("notes.txt") # get file size in byte
os.listdir(os.getcwd()) # ls of the current directory
os.path.exists(path) # checks a path exists
os.path.isdir(path) 
os.path.isfile(path)

Open/Read/Write file

# read file
file = open("notes.txt")
content = file.read()
file.close()

# read line by lines
file = open("notes.txt")
content = file.readlines()
for line in content:
    print(line)
file.close()

# alternative reading file line by line

with open('file.txt') as f:
    lines = f.readlines()
for line in lines:
    print(line)
f.close()

# write to file
file = open("notes.txt", "w")
file.write("Something") # it overwrites all the content
file.close()

# alternative write to file
o = open("file.txt", "a")
o.write("{colum1}, {column2}, {column3}\n".format(column1="A", column2="B", column3="C"))
o.close()

# append to file
file = open("notes.txt", "a")
file.write("Append") # it appends to the current file and not overwriting the content
file.close()

Shelve configuration files

import shelve

sfile = shelve.open('config')
sfile['key'] = ['v1', 'v2', 'v3']
sfile.close()

list(sfile.keys()) # returns `key`
list(sfile.values()) # returns `['v1', 'v2', 'v3']`
sfile.get('key') # returns `['v1', 'v2', 'v3']`
sfile.pop('key') # returns `['v1', 'v2', 'v3']` and remove the entery from the file

Copy, move, delete, listing files

import shutil
import os

shutil.copy("source", "target") # copy a file
shutil.copytree("source", "target") # copy a directory recursive with all files and sub-directories
shutil.move("source", "target")
os.unlink("file") # permanently deletes a file
os.rmdir("directory") # deletes an empty directory
shutil.rmtree("directory") # deletes an entire directory with its contents

# sending the file to trash
import send2trash
send2trash.send2trash("file")

# walking path
for directory_name, sub_directories, files in os.walk(os.getcwd()):
    print("Current directory" + directory_name)
    for sub_directory in sub_directories:
        print("Sub directory of " + directory_name + " is : " + sub_directory)
    for file in files:
        print(directory_name + "/" + sub_directory + "/" + file)

Zip files

import zipfile

# read content of a zip file
file = zipfile.ZipFile("test.zip")
file.namelist()
file.close()

# extract zip file contents
file = zipfile.ZipFile("z.zip")
file.extractall()
file.close()

# creating a zip file
file = zipfile.ZipFile("z.zip", "w")
file.write("note.txt", compress_type=zipfile.ZIP_DEFLATED)
file.write("picture.jpg", compress_type=zipfile.ZIP_DEFLATED)
file.close()

Difference between `class Name:` and `class Name(object):`

# the old syntax prior to python 2.2
class Test:

# new synatx recommended after python 2.2
# supports metadata
# supports getters and setter
class Test(object):

Exception handling

try:
    raise Exception("A test exceptioin") # throw an exception
except Exception as ex:
    print(ex) # catches the exception and prints the message

Logging

import logging
logging.basicConfig(level=logging.DEBUG, format=' %(asctime)s - %(levelname)s - %(message)s')
# log to a file
logging.basicConfig(filename = "prog.log", level=logging.DEBUG, format=' %(asctime)s - %(levelname)s - %(message)s')

logging.debug("DEBUG LOG")
logging.info("INFO LOG")
logging.warn("WARNING LOG")
logging.error("ERROR LOG")
logging.critical("FATAL LOG")
logging.disable(logging.DEBUG) # disable debug log

HTTP requests

import requests

# simple get request
url = "http://weather-api.madadipouya.com/v1/weather/currentbyip"
response = requests.get(url)
if response.ok and response.status_code == 200:
    json = response.json()
    print(json['country'])

# get request with param
url = "http://weather-api.madadipouya.com/v1/weather/currentbyip"
response = requests.get(url, params = {"fahrenheit": "true"})
# it would be equal to http://weather-api.madadipouya.com/v1/weather/currentbyip?fahrenheit=true"

# get request with custom headers
url = "http://weather-api.madadipouya.com/v1/weather/currentbyip"
response = requests.get(url, params = {"fahrenheit": "true"}, headers = {"user-agent": "my-app/0.0.1"})

# post request (form)
url = "https://httpbin.org/post"
response = requests.post(url, data = {"first_name": "John", "last_name": "Wick", "age": 31}, params = {"page_number": 0})

# post request (json)
import json
url = "https://httpbin.org/post"
response = requests.post(url, data = json.dumps({"first_name": "John", "last_name": "Wick", "age": 31}), params = {"page_number": 0}, headers = {"user-agent": "Test"})
# or added in version 2.4.2
response = requests.post(url, json = {"first_name": "John", "last_name": "Wick", "age": 31}, params = {"page_number": 0}, headers = {"user-agent": "Test"})

Working with CSV

import csv

file = open("file.csv")
reader = csv.reader(file)
content = list(reader) # content of csv file in list
file.close()

# reading csv line by line

for line in reader:
    print("line number: " + reader.line_num + " " + line)

# writing to a csv file

file = open("file.csv")
writer = csv.writer(file)
writer.writerow(['id', 'first_name', 'last_name'])
writer.writerow(['1', 'John', 'Wick'])
file.close()

# custom delimiter
cv.writer(file, delimiter='\t', lineterminator='\n\n')

Working with JSON

import json

# string to json object
json_string = '{"id": 1, "first_name": "John", "last_name": "Wick"}'
json_object = json.loads(json_string)

# json object to string
new_json_string = json.dumps(json_object)
isinstance(new_json_string, str) # returns true

Reading terminal arguments

import sys

if len(sys.argv < 2):
    print("No argument passed")
    sys.exit()
arg1 = sys.argv[1]
arg_array = sys.argv[1:]

Date and Time

import time
import datetime
time.time() # epoch time in seconds
time.sleep(5) # sleeps for 5 seconds

dt = datetime.datetime.now()
dt.year
dt.month
dt.day
dt.hour
dt.minute
dt.second
old_dt = datetime.datetime(2000, 12, 27, 22, 10, 30)
old_dt > dt # return false

duration = datetime.timedelta(days=20, hours=1, minutes=2, seconds=40)
delta.total_seconds() # returns the duration in seconds
dt = datetime.datetime.strptime('2015/10/21 16:29:00', '%Y/%m/%d %H:%M:%S') # string to date time

Multithreading

import threading

def print_hello_world():
    print("Hello World!")

def multiple(x, y):
    print(x*y)
thread_hello = threading.Thread(target=print_hello_world)
thread_hello.start()
thread_multiple = threading.Thread(target=multiple, args = [10, 20])
thread_multiple.start()

# thread join
threads = [thread_hello, thread_multiple]
for thread in threads:
    thread.join()

# thread pooling
from concurrent.futures.thread import ThreadPoolExecutor
thread_pool = ThreadPoolExecutor(5)
thread_pool.submit(print_hello_world)
thread_pool.submit(multiple, 10, 20)

# subprocess
import subprocess
chromium = subprocess.Popen("chromium-browser") # opens chromium
subprocess.Popen(["chromium-browser", "youtube.com"]) # subprocess with argument
chromium.wait() # waits until chromium to close
chromium.poll() # whether the subprocess is still running

Mouse and keyboard control

import pyautogui
pyautogui.size() # get screen size
pyautogui.moveTo(100, 200, duration=0.25) # move a mouse
pyautogui.position() # mouse position x, y coordinates
pyautogui.click(button='left') # mouse left click current coordinates
pyautogui.click(200, 250, button='left') # mouse left click custom coordinates
pyautogui.click(200, 250, button='right') # mouse right click
pyautogui.dragTo() # drag and drop
pyautogui.dragRel() # drag and drop
pyautogui.scroll(50) # scroll
im = pyautogui.screenshot() # take screen shot

# click on an icon that we only have image of it
coordinates = pyautogui.locateOnScreen('submit.png') # pass icon image for getting its coordinates with image recognition (10, 20, 50, 100)
center = pyautogui.center(coordinates) # get center of the icon (70, 20)
pyautogui.click(center)

# typing with keyboard
pyautogui.typewrite("HI")
pyautogui.typewrite(["Hello", "enter", "shiftleft", "world"]) # prints Hello \n World
pyautogui.keyDown("shift")
pyautogui.press("4")
pyautogui.keyUp("shift")
pyautogui.hotkey("altleft", "f4") # executing a hotkey

Working with pip

`pip install --user youtube-dl`	Installs Youtube-dl in user space
`pip install --user --upgrade youtube-dl`	Updates Youtube-dl
`pip uninstall youtube-dl`	Removes Youtube-dl

Scaffold a project with pip

Install virtualenv

$ python3 -m pip install --user virtualenv

Create project directory

$ mkdir myproject && cd myproject

Create virtualenv

$ python3 -m venv env

Activate virtualenv

$ source env/bin/activate

Ensure virtualenv is working

$ which python # should point to a virtualenv path

Install packages

$ pip3 install [package name] # e.g., pip3 install python-socketio

Save installed packages to requirements.txt file

$ pip3 freeze > requirements.txt

Install all packages from requirements.txt

$ pip3 install -r requirements.txt

Leave virtualenv

$ deactivate

Sources

Automate the Boring Stuff with Python

Shortcuts

Basics

ABC Basics

Import

Multi Import

Different Import approaches

Print

String interpolation

String manipulation

Pattern matching

List

Dictionary

keys(), values(), items(), get(), setdefault() in a dictionary

Conditions

Loop

Class

Inheritance

Abstract Base Class (ABC) or Interface

Get and initialize subclasses of a class

Get type and type comparison

Interaction with pip

Working with files

OS path

Open/Read/Write file

Shelve configuration files

Copy, move, delete, listing files

Zip files

Difference between class Name: and class Name(object):

Exception handling

Logging

HTTP requests

Working with CSV

Working with JSON

Reading terminal arguments

Date and Time

Multithreading

Mouse and keyboard control

Working with pip

Scaffold a project with pip

Sources

Difference between `class Name:` and `class Name(object):`