Python 3 Cheat Sheet

In Python

Python 3 is the latest version of the popular programming language, Python. It was released in 2008 and has since become the preferred version for many developers. Python 3 is an improvement over Python 2, with new features and enhancements that make it more powerful and easier to use.

One of the most significant changes in Python 3 is the way it handles strings. In Python 2, strings were represented as ASCII characters, which limited the range of characters that could be used. Python 3, on the other hand, uses Unicode, which allows for a much broader range of characters, including non-Latin characters.

Another major change in Python 3 is the print function. In Python 2, the print statement was used to output text to the console. In Python 3, the print function is used instead, which makes it easier to format output and avoid errors.

This cheat sheet provides a quick reference for some of the most commonly used Python 3 syntax and functions.

Table of Contents

Variables and Data Types

x = 5Assigns the value 5 to the variable x
x = ""hello""Assigns the string ""hello"" to the variable x
x = TrueAssigns the boolean value True to the variable x
x = NoneAssigns the value None to the variable x
type(x)Returns the data type of x
int(x)Converts x to an integer
float(x)Converts x to a float
str(x)Converts x to a string
bool(x)Converts x to a boolean
list(x)Converts x to a list
dict(x)Converts x to a dictionary


//Floor division
<Less than
>Greater than
<=Less than or equal to
>=Greater than or equal to
andLogical and
orLogical or
notLogical not

Control Flow

if condition:Executes the code block if the condition is true
elif condition:Executes the code block if the previous condition(s) were false and this condition is true
else:Executes the code block if all previous conditions were false
for variable in iterable:Loops through each item in the iterable, assigning it to the variable
while condition:Loops through the code block as long as the condition is true
breakExits the current loop
continueSkips the current iteration of the loop
passDoes nothing (used as a placeholder)


def function_name(parameters):Defines a function with the given name and parameters
return valueReturns the value from a function
lambda parameters: expressionDefines an anonymous function with the given parameters and expression


my_list = []Creates an empty list
my_list = [1, 2, 3]Creates a list with the given values
my_list.append(value)Adds the value to the end of the list
my_list.insert(index, value)Inserts the value at the given index
my_list.remove(value)Removes the first occurrence of the value from the list
my_list.pop(index)Removes and returns the value at the given index
my_list.index(value)Returns the index of the first occurrence of the value
my_list.count(value)Returns the number of times the value appears in the list
my_list.sort()Sorts the list in ascending order
my_list.reverse()Reverses the order of the list


my_dict = {}Creates an empty dictionary
my_dict = {""key"": ""value""}Creates a dictionary with the given key-value pair
my_dict[key] = valueAdds or updates the key-value pair in the dictionary
del my_dict[key]Removes the key-value pair with the given key
my_dict.keys()Returns a list of all the keys in the dictionary
my_dict.values()Returns a list of all the values in the dictionary
my_dict.items()Returns a list of all the key-value pairs in the dictionary


my_string = """"Creates an empty string
my_string = ""hello""Creates a string with the given value
len(my_string)Returns the length of the string
my_string.upper()Returns a new string with all uppercase letters
my_string.lower()Returns a new string with all lowercase letters
my_string.capitalize()Returns a new string with the first letter capitalized
my_string.replace(old, new)Returns a new string with all occurrences of the old string replaced with the new string
my_string.split(separator)Returns a list of substrings separated by the given separator
my_string.join(iterable)Returns a new string by concatenating the elements of the iterable with the string

File I/O

file = open(filename, mode)Opens the file with the given filename and mode the contents of the file as a string
file.readline()Returns the next line of the file as a string
file.readlines()Returns a list of all the lines in the file
file.write(string)Writes the string to the file
file.close()Closes the file


import module_nameImports the module with the given name
from module_name import function_nameImports the specified function from the module
from module_name import *Imports all functions from the module
module_name.function_name()Calls the specified function from the module


Python 3 Documentation