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Abhiraj Bhowmick
Abhiraj Bhowmick

Posted on • Originally published at abhirajb.hashnode.dev

The Ultimate Python Cheatsheet

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")
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Taking Input From User
the input function is used to take input from the user

var1 = input("Enter your name: ")
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Empty List
This method allows you to create an empty list

my_list = []
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Empty Dictionary
By putting two curly braces, you can create a blank dictionary

my_dict = {}
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Range Function
range function returns a sequence of numbers, eg, numbers starting from 0 to n-1 for range(0, n)

range(int_value)
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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
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Multi-line comment

'''This is a
multi-line
comment'''
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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
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Backslash
It adds a backslash

\\
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Single Quote
It adds a single quotation mark

\'
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Tab
It gives a tab space

\t
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Backspace
It adds a backspace

\b
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Octal value
It represents the value of an octal number

\ooo
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Hex value
It represents the value of a hex number

\xhh
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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
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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"
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Slicing
Slicing refers to obtaining a sub-string from the given string.

var_name[n : m]
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String Methods isalnum() method
Returns True if all characters in the string are alphanumeric

string_variable.isalnum()
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isalpha() method
Returns True if all characters in the string are alphabet

string_variable.isalpha()
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isdecimal() method
Returns True if all characters in the string are decimals

string_variable.isdecimal()
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isdigit() method
Returns True if all characters in the string are digits

string_variable.isdigit()
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islower() method
Returns True if all characters in the string are lower case

string_variable.islower()
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isspace() method
Returns True if all characters in the string are whitespaces

string_variable.isspace()
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isupper() method
Returns True if all characters in the string are upper case

string_variable.isupper()
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lower() method
Converts a string into lower case

string_variable.lower()
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upper() method
Converts a string into upper case

string_variable.upper()
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strip() method
It removes leading and trailing spaces in the string

string_variable.strip()
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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]
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List Methods index method
Returns the index of the first element with the specified value

list.index(element)
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append method
Adds an element at the end of the list

list.append(element)
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extend method
Add the elements of a list (or any iterable) to the end of the current list

list.extend(iterable)
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insert method
Adds an element at the specified position

list.insert(position, element)
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pop method
Removes the element at the specified position and returns it

list.pop(position)
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remove method
The remove( ) method removes the first occurrence of a given item from the list

list.remove(element)
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clear method
Removes all the elements from the list

list.clear()
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count method
Returns the number of elements with the specified value

list.count(value)
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reverse method
Reverse the order of the list

list.reverse()
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sort method
Sorts the list

list.sort(reverse=True|False)
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Tuples
Tuples are represented as a list of comma-separated values of any data type within parentheses.

Tuple Creation

variable_name = (element1, element2, ...)
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Tuple Methods count method
It returns the number of times a specified value occurs in a tuple

tuple.count(value)
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index method
It searches the tuple for a specified value and returns the position.

tuple.index(value)
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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, ...}
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Set Creation: Way 2

var_name = set([element1, element2, ...])
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Set Methods: add() method
Adds an element to a set

set.add(element)
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clear() method
Remove all elements from a set

set.clear()
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discard() method
Removes the specified item from the set

set.discard(value)
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intersection() method
Returns intersection of two or more sets

set.intersection(set1, set2 ... etc)
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issubset() method
Checks if a Set is Subset of Another Set

set.issubset(set)
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pop() method
Removes an element from the set

set.pop()
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remove() method
Removes the specified element from the Set

set.remove(item)
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union() method
Returns the union of Sets

set.union(set1, set2...)
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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 ...}
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Adding Element to a dictionary
By this method, one can add new elements to the dictionary

<dictionary>[<key>] = <value>
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Updating Element in a dictionary
If the specified key already exists, then its value will get updated

<dictionary>[<key>] = <value>
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Deleting Element from a dictionary
del let to delete specified key: value pair from the dictionary

del <dictionary>[<key>]
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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)
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clear() method
Removes all the elements from the dictionary

dictionary.clear()
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get() method
Returns the value of the specified key

dictionary.get(keyname)
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items() method
Returns a list containing a tuple for each key-value pair

dictionary.items()
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keys() method
Returns a list containing the dictionary's keys

dictionary.keys()
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values() method
Returns a list of all the values in the dictionary

dictionary.values()
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update() method
Updates the dictionary with the specified key-value pairs

dictionary.update(iterable)
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Conditional Statements
The if statements are the conditional statements in Python, and these implement selection constructs (decision constructs).

if Statement

if(conditional expression):
   statements
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if-else Statement

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

if (conditional expression) :
    statements
elif (conditional expression) :
    statements
else :
    statements
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Nested if-else Statement

if (conditional expression):
   statements
else:
   statements
else:
   statements
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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
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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
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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
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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
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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
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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")
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close() function

var_name.close()
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Read () function
The read functions contains different methods, read(),readline() and readlines()

read() #return one big string
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It returns a list of lines

read-lines
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It returns one line at a time

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

write () #Used to write a fixed sequence of characters to a file
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It is used to write a list of strings

writelines()
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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")
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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]
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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
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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)
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object
Instantiating an object

<object-name> = <class-name>(<arguments>)
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filter function
The filter function allows you to process an iterable and extract those items that satisfy a given condition

filter(function, iterable)
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issubclass function
Used to find whether a class is a subclass of a given class (classinfo) or not

issubclass(class, classinfo)
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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))
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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
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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
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setter Decorator
It is used to set the property 'name'

@name.setter
def name(self, value):
self.__name=value
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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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Discussion (5)

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ejm profile image
EJM97

There seems to be an syntax issue in the Nested if-else Statement. 1 if but 2 else statements.

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abhirajb profile image
Abhiraj Bhowmick Author

That is not a syntax error. That is called nesting in computer programming. Any number of these statements can be nested inside one another. If I would give only one else statement then there would not be any difference between nested statements and normal if-else statements
Hope I was able to clear it for you :)

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ejm profile image
EJM97

Apprecieate the explanation, but unfortunately I still don't get it. Could you please explain further, my current understanding of nested if statements is as follows.

if condition 1:
    statements
    # a nested if-else
    if condition 2:
        statements
    else:
        statements
else:
    statements
    # another nested if-else     
    if condition 3:
        statements
    else:
        statements    

I tried using 2 else statements witihn one 'if' indented in diferrent ways but it always threw an error.
for exaple i tried -->

if condition 1:
    statements
    else:
        statements
else:
    statements

Using 2 else statements after a single if seems logically pointless even if it were syntactically correct as all the statements under both else conditions seems to be executed only when the if condition is False    

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tngeene profile image
Ted Ngeene

Nice article! For the conditional statements bit, could you show the indentation. Since this is meant for beginners, I feel it would be important to indent the examples.

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michaelcurrin profile image
Michael

And the classes need indentation too