The Ultimate Python Cheatsheet

The Ultimate Python Cheatsheet

Abhiraj Bhowmick
·Sep 21, 2021·

9 min read

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The Ultimate 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):
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

It returns a list of lines

read-lines

It returns one line at a time

readline

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

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

It is used to write a list of strings

writelines()

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

Deletor Decorator It is used to delete the property 'name'

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

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