In this post you will find a very handy Python memory aid
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Here is my cheat sheet I created along my learning journey. If you have any recommendations (addition/subtraction) let me know.
Python Cheat Sheet
Naming conventions
# Variable lower_snake
first_name = 'Mike'
# Class and module CamelCase
class InvoiceDetail:
# Constant
MAX_USER = 100 # All uppercase
# Indentation : 4 spaces
if num > 9:
print('Small number')
Data type
name = 'Mike' # string
age = 42 # int
price = 199.99 # float
is_active = True # boolean
colors = ['red', 'green', 'blue'] # list
states = ('inactive', 'active', 'archive') # tuple
products = { 'name': 'iPad Pro', 'price': 199.99 } # dict
Type conversion
# Python is a strong type language
number = 50 + "50" # TypeError
# Convert to string
number = 50 + int("50") # 100
# Convert to string
my_text = str(199.99) # "199.99"
# Convert to number
my_number = int(21.99) # 21
my_number = float('21.99') # 21.99
# Get type
type(my_text) # <class 'str'>
type(my_number) # <class 'float'>
# Check if number 0 to 9
isdigit('8') # True
# Check type
isinstance(my_number, int) # True
Strings
name = 'Mike'
# or
name = "Mike"
# or
message = """This is multiline
string that is easier to
read and assign"""
# escape characters \n will do a line break
message = "Hello \nWorld"
# raw string (ignore escape characters)
message = r"https:\\example.com\index.html"
# Convert to lower case
name.lower() # mike
# Convert to upper case
name.upper() # MIKE
# Convert first char to Capital letter
name.capitalize() # Mike
# Convert first char of all words to Capital letter
name = 'mike taylor'
name.title() # Mike Taylor
# Chain methods
name = 'MIKE'
name.lower().capitalize() # Mike
name = 'Mike'
# Start with ?
name.startswith('M') # true
# End with ?
name.endswith('ke') # true
# String length
len(name) # 4
# String concatenation
full_name = first_name + ' ' + last_name
# String format
full_name = f"{first_name} {last_name}"
# String format number (2 decimal point)
number = 12.9997
number_string = "{:.2f}".format(number) # '12.99'
# Remove leading and trailing characters (like space or \n)
text = ' this is a text with white space '
text.strip() # 'this is a test with white space'
name = 'Mike'
# Get string first character
name[0] # M
# Get string last character
name[-1] # e
# Get partial string
name[1:3] # ik
# Replace
name.replace('M', 'P') # Pike
# Find (return pos or -1 if not found)
name.find('k') # 2
# List to string
colors = ['red', 'green', 'blue']
', '.join(colors) # 'red, green, blue'
Commons fonctions
# Print to console
print('Hello World')
# Print multiple string
print('Hello', 'World') # Hello World
# Multiple print
print(10 * '-') # ----------
# Variable pretty printer (for debug)
from pprint import pprint
pprint(products) # will output var with formatting
# Get keyboard input
name = input('What is your name? ')
# Random (between 0 and 1)
from random import random
print(random()) # 0.26230234411558273
# Random beween x and y
from random import randint
print(randint(3, 9)) # 5
# Rounding
number = 4.5
print(round(number)) # 5
number = 4.5163
print(round(number, 2)) # 4.52
# Path
import os
current_file_path = __file__
folder_name = os.path.dirname(current_file_path)
new_path = os.path.join(folder_name, 'new folder')
# Round number
solution = round(12.9582, 2) # 12.96
Conditionals
if x == 4:
print('x is 4')
elif x != 5 and x < 11:
print('x is between 6 and 10')
else:
print('x is 5 or greater than 10')
#In or not in
colors = ['red', 'green', 'blue', 'yellow']
if 'blue' in colors:
if 'white' not in colors:
# Ternary
print('y = 10') if y == 10 else print('y != 10')
# ShortHand Ternary
is_valid = 'Valid'
msg = is_valid or "Not valid" # 'Valid'
# Falsy
False, None, 0, empty string "", empty list [], (), {}
# Truthy
True, not zero and not empty value
Interations
# iterating over a sequence (list, string, etc.)
for item in items:
print(item)
# With index
for index, item in enumerate(items):
print(index, item)
# Range
for i in range(10): #0..9
print(i)
for i in range(5, 10): #5..9
print(i)
# While loop
while x > 10:
print(x)
# exit loop
if x == 5:
break
# Jump to next while
if x == 3:
continue
x += 1
# For loop dic
for key, value in my_dict.items():
print(key, value)
# List comprehension:
# values = [(expression) for (value) in (collection)]
items = [value*2 for value in items]
# List comprehension filtering
# values = [expression for value in collection if condition]
even_squares = [x * x for x in range(10) if x % 2 == 0]
List and Tuple
# Create a list
fruits = ['orange', 'apple', 'melon']
# Append to List
fruits.append('banana')
# List length
nb_items = len(fruits)
# Remove from list
del fruits[1] #remove apple
# List access
fruits[0] # first item
fruits[-1] # last item
# Slice my_list[start:finish:step] ([::-1] reverse list)
fruits = fruits[1:3]
fruits[:3] # first 3
fruits[2:] # last 2
copy_fruits = fruits[:] # copy
# List length
nb_entry = len(fruits)
#Create list from string
colors = 'red, green, blue'.split(', ')
# Array concact
color1 = ['red', 'blue']
color2 = ['green', 'yellow']
color3 = color1 + color2
# Concat by unpacking
color3 = [*color1, *color2]
# Multiple assignment
name, price = ['iPhone', 599]
#Create a Tuple (kind of read only list)
colors = ('red', 'green', 'blue')
# Sort
colors.sort() # ['blue', 'green', 'red']
colors.sort(reverse=True) # ['red', 'green', 'blue']
colors.sort(key=lambda color: len(color)) # ['red', 'blue', 'green']
Dictionaries
# Create a empty dict
product = {}
#Create a dict with key/value
product = {'id': 100, 'name': 'iPadPro'}
# Access dict value by key
print(product['name']) # iPadPro
# Access dict
product.get('name') # if key not exist return None
product.get('name', 'default value') # if key not exist return default value
# Adding a new key/value
product['description'] = "Modern mobile device"
# Get dict keys
product.keys() # ['id', 'name', 'description']
# Get dic values
product.values() # ['100', 'iPadPro', 'Modern mobile device']
# Create a list of dict
products = [
{'id': 100, 'name': 'iPadPro'},
{'id': 200, 'name': 'iPhone 12'},
{'id': 300, 'name': 'Charger'},
]
# Access list of dict
print(products[2]['name']) # Charger
# Search list dict
items_match = [item for product in products if product['id'] == 300]
# [{'id': 300, 'name': 'Charger'}]
# Sum list dict
total = sum([product['price'] for product in products])
Functions
# Create a function
def say_hello():
print('Hello World')
# Function with argument (with default value)
def say_hello(name = 'no name'):
print(f"Hello {name}")
# Function with argument (with optional value)
def say_hello(name = None):
if name:
print(f"Hello {name}")
else:
print('Hello World')
# Call a function
say_hello('Mike') # Hello Mike
# Call using keyword argument
say_hello(name = 'Mike')
# Function returning a value
def add(num1, num2):
return num1 + num2
num = add(10, 20) # 30
# Arbitrary numbers of arguments *args
def say_hello(*names):
for name in names:
print(f"Hello {name}")
# Arbitrary numbers of keywords arguments **kwargs
def say_hello(**kwargs):
print(kwargs['name'])
print(kwargs['age'])
say_hello(name = 'Mike', age = 45)
# Lambda function
x = lambda num : num + 10
print(x(20)) # 30
Date and time
from datetime import datetime, timedelta
# Return the current date and time.
datetime.now()
# Create a date time object
date = datetime(2020,12,31) # Dec 31 2020
# Add to date/time (weeks, days, hours, minutes, seconds)
new_year = date + timedelta(days=1) # Jan 1 2021
# Format a date to string
new_year.strftime('%Y/%m/%d %H %M %S') # 2021/01/01 00 00 00
new_year.strftime('%A, %b %d') # Friday, Jan 01
# Extract from date
year = new_year.year # 2021
month = new_year.month # 01
File
# Reading a file and storing its lines
filename = 'demo.txt'
with open(filename) as file:
lines = file.readlines()
for line in lines:
print(line)
# Writing to a file
filename = 'settings.txt'
with open(filename, 'w') as file:
file.write("MAX_USER = 100")
# File exist?
from os import path
path.exists('templates/index.html') # True/False
# CSV
import csv
csv_file = 'export.csv'
csv_columns = products[0].keys() # ['id', 'name']
with open(csv_file, 'w') as csvfile:
writer = csv.DictWriter(csvfile, fieldnames=csv_columns)
writer.writeheader()
for item in products:
writer.writerow(item)
Catching an exception
age_string = input('Your age? ')
try:
age = int(age_string)
except ValueError:
print("Please enter a numeric value")
else:
print("Your age is saved!")
OOP
# Create a class
class Product:
pass
# Class attribute
class Product:
nb_products = 0
print(Product.nb_products) # 0
# Create new object instance
product_1 = Product()
# Object instance attributes
class Product:
def __init__(self, name, price):
self.name = name
self.price = price
# Create instance with attributes
product_1 = Product('iPadPro', 699.99)
product_2 = Product('iPhone12', 799.99)
print(product_1.name) # iPadPro
# instance method
class Product()
def display_price(self):
return f"Price : {self.price}"
print(product_1.display_price())
# class method
class Product:
# ...
@classmethod
def create_default(cls):
# create a instance
return cls('Product', 0) # default name, default price
product_3 = Product.create_default()
# static method
class Product:
# ...
@staticmethod
def trunc_text(word, nb_char):
return word[:nb_char] + '...'
product_3 = Product.trunc_text('This is a blog', 5) # This i...
# Python Inheritance
class WebProduct(Product):
def __init__(self, name, price, web_code):
super().__init__(name, price)
self.web_code = web_code
# Private scope (naming convention only)
def __init__(self, price):
self.__price = price
# Getter and setter
class Product:
def __init__(self):
self.__price = 0
@property
def price(self):
return self.__price
@price.setter
def price(self, value):
self.__price = value
# Mixins
class Mixin1(object):
def test(self):
print "Mixin1"
class Mixin2(object):
def test(self):
print "Mixin2"
class MyClass(Mixin2, Mixin1, BaseClass):
pass
obj = MyClass()
obj.test() # Mixin2
Module import
from my_module import my_function
# import local file (same folder)
# my_module.py will be the file name
# my_function is a function inside my_module.py
Dont miss my next python post: Follow @EricTheCoder_
Here is my cheat sheet I created along my learning journey. If you have any recommendations (addition/subtraction) let me know.
Top comments (4)
Great work!
Some suggestions for improvement:
int('21.99')
won't convert it to an integer. It will raise aValueError
. To convert the string of21.99
to an int, you need to do thisint(float('21.99'))
, which will result in 21MAX_USER = 100
isn't a "const" data type. Constants are a concept vs a data typeYou could expand the data types to include another very common Python data structure, the good old tuple. e.g.
(1,2,3,4)
. Plus, you may also want to include sets, e.g.{1, 2, 3}
I didn't read any further, but thought I'd point out those couple of quick items that I noticed.
All the best
Convert to string
number = 50 + int("50") # 100
isn't it conversion to int?
Good Job!
BTW, Eric the Coder, meet Roger the Shruber ;)
excellent