Python Cheatsheet

Basics

Basic syntax from the python programming language

• Showing Output To User: the print function is used to display or print output

print("Content that you wanna print on screen")

• Taking Input From User: the input function is used to take input from the user

var1 = input("Enter your name: ")

• Empty List: This method allows you to create an empty list

my_list = []

• Empty Dictionary: By putting two curly braces, you can create a blank dictionary

my_dict = {}

• Range Function: range function returns a sequence of numbers, eg, numbers starting from 0 to n-1 for range(0, n)

range(int_value)

Comments

Comments are used to make the code more understandable for programmers, and they are not executed by compiler or interpreter.

Single line comment

#This is a single line comment

Multi-line comment

'''This is a
multi-line
comment'''

Escape Sequence

An escape sequence is a sequence of characters; it doesn't represent itself when used inside string literal or character.

Newline (Newline Character)

\n

Backslash (It adds a backslash)

\\

Single Quote (It adds a single quotation mark)

\'

Tab (It gives a tab space)

\t

Backspace (It adds a backspace)

\b

Octal value (It represents the value of an octal number)

\ooo

Hex value (It represents the value of a hex number)

\xhh

Carriage Return

Carriage return or \r is a unique feature of Python. \r will just work as you have shifted your cursor to the beginning of the string or line.

\r

Strings

Python string is a sequence of characters, and each character can be individually accessed. Using its index.

String: You can create Strings by enclosing text in both forms of quotes - single quotes or double-quotes.

variable_name = "String Data"

Slicing: Slicing refers to obtaining a sub-string from the given string.

var_name[n : m]

String Methods

• isalnum() method: Returns True if all characters in the string are alphanumeric

string_variable.isalnum()

• isalpha() method: Returns True if all characters in the string are alphabet

string_variable.isalpha()

• isdecimal() method: Returns True if all characters in the string are decimals

string_variable.isdecimal()

• isdigit() method: Returns True if all characters in the string are digits

string_variable.isdigit()

• islower() method: Returns True if all characters in the string are lower case

string_variable.islower()

• isspace() method: Returns True if all characters in the string are whitespaces

string_variable.isspace()

• isupper() method: Returns True if all characters in the string are upper case

string_variable.isupper()

• lower() method: Converts a string into lower case

string_variable.lower()

• upper() method: Converts a string into upper case

string_variable.upper()

• strip() method: It removes leading and trailing spaces in the string

string_variable.strip()

List

A List in Python represents a list of comma-separated values of any data type between square brackets.

List

var_name = [element1, element2, and so on]

List Methods

• index method: Returns the index of the first element with the specified value

list.index(element)

• append method: Adds an element at the end of the list

list.append(element)

• extend method: Add the elements of a list (or any iterable) to the end of the current list

list.extend(iterable)

• insert method: Adds an element at the specified position

list.insert(position, element)

• pop method: Removes the element at the specified position and returns it

list.pop(position)

• remove method: The remove( ) method removes the first occurrence of a given item from the list

list.remove(element)

• clear method: Removes all the elements from the list

list.clear()

• count method: Returns the number of elements with the specified value

list.count(value)

• reverse method: Reverse the order of the list

list.reverse()

• sort method: Sorts the list

list.sort(reverse=True|False)

Tuples

Tuples are represented as a list of comma-separated values of any data type within parentheses.

Tuple Creation

variable_name = (element1, element2, ...)

Tuple Methods

• count method: It returns the number of times a specified value occurs in a tuple

tuple.count(value)

• index method: It searches the tuple for a specified value and returns the position.

tuple.index(value)

Sets

A set is a collection of multiple values which is both unordered and unindexed. It is written in curly brackets.

Set Creation: Way 1

var_name = {element1, element2, ...}

Set Creation: Way 2

var_name = set([element1, element2, ...])

Set Methods

• add() method: Adds an element to a set

set.add(element)

• clear() method: Remove all elements from a set

set.clear()

• discard() method: Removes the specified item from the set

set.discard(value)

• intersection() method: Returns intersection of two or more sets

set.intersection(set1, set2 ... etc)

• issubset() method: Checks if a Set is Subset of Another Set

set.issubset(set)

• pop() method: Removes an element from the set

set.pop()

• remove() method: Removes the specified element from the Set

set.remove(item)

• union() method: Returns the union of Sets

set.union(set1, set2...)

Dictionaries

The dictionary is an unordered set of comma-separated key: value pairs, within {}, with the requirement that within a dictionary, no two keys can be the same.

Dictionary

<dictionary-name> = {<key>: value, <key>: value ...}

• Adding Element to a dictionary: By this method, one can add new elements to the dictionary

<dictionary>[<key>] = <value>

• Updating Element in a dictionary: If the specified key already exists, then its value will get updated

<dictionary>[<key>] = <value>

• Deleting Element from a dictionary: del let to delete specified key: value pair from the dictionary

del <dictionary>[<key>]

Dictionary Functions & Methods

• len() method: It returns the length of the dictionary, i.e., the count of elements (key: value pairs) in the dictionary

len(dictionary)

• clear() method: Removes all the elements from the dictionary

dictionary.clear()

• get() method: Returns the value of the specified key

dictionary.get(keyname)

• items() method: Returns a list containing a tuple for each key-value pair

dictionary.items()

• keys() method: Returns a list containing the dictionary's keys

dictionary.keys()

• values() method: Returns a list of all the values in the dictionary

dictionary.values()

• update() method: Updates the dictionary with the specified key-value pairs

dictionary.update(iterable)

Conditional Statements

The if statements are the conditional statements in Python, and these implement selection constructs (decision constructs).

• if Statement

if(conditional expression):
   statements

• if-else Statement

if(conditional expression):
   statements
else:
   statements

• if-elif Statement

if (conditional expression) :
    statements
elif (conditional expression) :
    statements
else :
    statements

• Nested if-else Statement

if (conditional expression):
   statements
else:
   statements
else:
   statements

Iterative Statements

An iteration statement, or loop, repeatedly executes a statement, known as the loop body, until the controlling expression is false (0).

• For Loop: The for loop of Python is designed to process the items of any sequence, such as a list or a string, one by one.

for <variable> in <sequence>:
statements_to_repeat

• While Loop: A while loop is a conditional loop that will repeat the instructions within itself as long as a conditional remains true.

while <logical-expression> :
loop-body

• Break Statement: The break statement enables a program to skip over a part of the code. A break statement terminates the very loop it lies within.

for <var> in <sequence> :
statement1
if <condition> :
break
statement2
statement_after_loop

• Continue Statement: The continue statement skips the rest of the loop statements and causes the next iteration to occur.

for <var> in <sequence> :
statement1
if <condition> :
continue
statement2
statement3
statement4

Functions

A function is a block of code that performs a specific task. You can pass parameters into a function. It helps us to make our code more organized and manageable.

Function Definition

def my_function(parameters):
# Statements

File Handling

File handling refers to reading or writing data from files. Python provides some functions that allow us to manipulate data in the files.

• open() function

var_name = open("file name", "opening mode")

• close() function

var_name.close()

• Read () function: The read functions contains different methods, read(),readline() and readlines()

read() # return one big string

read-lines # returns a list of lines

readline # returns one line at a time

• Write () function: This function writes a sequence of strings to the file.

write () # Used to write a fixed sequence of characters to a file

writelines() # Used to write a list of strings

• Append () function: The append function is used to append to the file instead of overwriting it. To append to an existing file, simply open the file in append mode (a):

file = open("Hello.txt", "a")

Exception Handling

An exception is an unusual condition that results in an interruption in the flow of the program.

try and except: A basic try-catch block in python. When the try block throws an error, the control goes to the except block.

try:
[Statement body block]
raise Exception()
except Exception as e:
[Error processing block]

OOPS

It is a programming approach that primarily focuses on using objects and classes. The objects can be any real-world entities.

• class: The syntax for writing a class in python

class class_name:
#Statements

• class with a constructor: The syntax for writing a class with the constructor in python

class Abhiraj: # Default constructor
def __init__(self):
self.name = "Abhiraj" # A method for printing data members
def print_me(self):
print(self.name)

• object: Instantiating an object

<object-name> = <class-name>(<arguments>)

• filter function: The filter function allows you to process an iterable and extract those items that satisfy a given condition

filter(function, iterable)

• issubclass function: Used to find whether a class is a subclass of a given class (classinfo) or not

issubclass(class, classinfo)

Iterators and Generators

Here are some of the advanced topics of the Python programming language like iterators and generators

• Iterator: Used to create an iterator over an iterable

iter_list = iter(['Harry', 'Aakash', 'Rohan']) 
print(next(iter_list)) 
print(next(iter_list)) 
print(next(iter_list))

• Generator: Used to generate values on the fly

# A simple generator function
def my_gen():
n = 1
print('This is printed first')
# Generator function contains yield statements
yield n
n += 1
print('This is printed second')
yield n
n += 1
print('This is printed at last')
yield n

Decorators

Decorators are used to modifying the behavior of function or class. They are usually called before the definition of a function you want to decorate.

• property Decorator (getter)

@property
def name(self):
return self.__name

• setter Decorator (It is used to set the property 'name')

@name.setter
def name(self, value):
self.__name=value

• deleter Decorator (It is used to delete the property 'name')

@name.deleter #property-name.deleter decorator
def name(self, value):
print('Deleting..')
del self.__name

Published: January 01, 2025

Python