Python CheatSheet

Basics Comments Escape Sequence Strings List Tuples Sets Dictionaries Indentation Conditional Statements Loops in Python Functions File Handling Exception Handling finally Object Oriented Programming (OOPS) Iterators and Generators Decorators 

Basics Showing Output To User Taking Input From the User range Function Comments Single line comment Multi-line comment Escape Sequence Newline Backslash Single Quote Tab Backspace Octal value Hex value Carriage Return Strings String Indexing Slicing isalnum() method isalpha() method isdecimal() method isdigit() method islower() method isspace() method isupper() method lower() method upper() method strip() method List Indexing Empty List index method append method extend method insert method pop method remove method clear method count method reverse method sort method Tuples Tuple Creation Indexing count method index method Sets Set Creation: Way 1 Set Creation: Way 2 Set Methods add() method clear() method discard() method intersection() method issubset() method pop() method remove() method union() method Dictionaries Dictionary Empty Dictionary Adding Element to a dictionary Updating Element in a dictionary Deleting an element from a dictionary Dictionary Functions & Methods len() method clear() method get() method items() method keys() method values() method update() method Indentation Conditional Statements if Statement if-else Statement if-elif Statement Nested if-else Statement Loops in Python For Loop While Loop Break Statement Continue Statement Functions Function Definition Function Call Return statement in Python function Arguments in python function File Handling open() function modes- close() function read () function write function Exception Handling try and except else finally Object Oriented Programming (OOPS) class Creating an object self parameter class with a constructor Inheritance in python Types of inheritance- filter function issubclass function Iterators and Generators Iterator Generator Decorators property Decorator (getter) setter Decorator deleter Decorator 

Basic syntax from the python programming language

Basics
 ⇧

 Showing Output To User
print("Content that you wanna print on screen")

var1 = "Shruti"
print("Hi my name is: ",var1)

 Taking Input From the User
var1 = input("Enter your name: ")
print("My name is: ", var1)

To take input as an integer:
var1=int(input("enter the integer value"))
print(var1)

To take input as an float:
var1=float(input("enter the float value"))
print(var1)

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

range(int_start_value,int_stop_value,int_step_value)
Here the start value and step value are by default 1 if not mentioned by the programmer. but int_stop_value is the compulsory parameter in range function
example
Display all even numbers between 1 to 100
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators


for i in range(0,101,2):
       print(i)

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
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

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

Escape Sequence
 ⇧

An escape sequence is a sequence of characters; it doesn't represent itself (but is translated into another character) when used inside string literal or character. Some of the escape sequence characters are as follows:

 Newline
Newline Character

print("\n")

 Backslash
It adds a backslash

print("\\")

 Single Quote
It adds a single quotation mark

print("\'")

 Tab
It gives a tab space

print("\t")

 Backspace
It adds a backspace

print("\b")

 Octal value
It represents the value of an octal number

print("\ooo")

 Hex value
It represents the value of a hex number

print("\xhh")

 Carriage Return
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

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

pint("\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"
example

str="Shruti"
print("string is ",str)

 Indexing
The position of every character placed in the string starts from 0th position ans step by step it ends at length-1 position

 Slicing
Slicing refers to obtaining a sub-string from the given string. The following code will include index 1, 2, 3, and 4 for the variable named var_name
Slicing of the string can be obtained by the following syntax

string_var[int_start_value:int_stop_value:int_step_value]

var_name[1 : 5]
here start and step value are considered 0 and 1 respectively if not mentioned by the programmmer

 isalnum() method
Returns True if all the characters in the string are alphanumeric, else False

string_variable.isalnum()

 isalpha() method
Returns True if all the characters in the string are alphabets

string_variable.isalpha()

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

string_variable.isdecimal()

 isdigit() method
Returns True if all the 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 equivalent

string_variable.lower()

 upper() method
Converts a string into upper case equivalent

string_variable.upper()

 strip() method
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

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.

var_name = [element1, element2, ...]
These elements can be of different datatypes

 Indexing
The position of every elements placed in the string starts from 0th position ans step by step it ends at length-1 position
List is ordered,indexed,mutable and most flexible and dynamic collection of elements in python.

 Empty List
This method allows you to create an empty list

my_list = []

 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 given 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
Reverses the order of the list

list.reverse()

 sort method
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

Sorts the list

list.sort(reverse=True|False)

Tuples
 ⇧

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

 Tuple Creation
variable_name = (element1, element2, ...)
These elements can be of different datatypes

 Indexing
The position of every elements placed in the string starts from 0th position ans step by step it ends at length-1 position
Tuples are ordered,indexing,immutable and most secured collection of elements
Lets talk about some of the tuple methods:

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

tuple.count(value)

Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

 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 is unordered,immutable,non-indexed type of collection.Duplicate elements are not allowed in sets.

 Set Methods
Lets talk about some of the methods of sets:

 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 a 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
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

Returns the union of two or more 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 ...}
Dictionary is ordered and mutable collection of elements.Dictionary allows duplicate values but not duplicate keys.

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

mydict={}

 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 a specified key already exists, then its value will get updated

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

 Deleting an element from a dictionary
del keyword is used to delete a specified key:value pair from the dictionary as follows:

del <dictionary>[<key>]

 Dictionary Functions & Methods
Below are some of the methods of dictionaries

 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()

Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

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

Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

dictionary.update(iterable)
Indentation
 ⇧

In Python, indentation means the code is written with some spaces or tabs into many different blocks of code to indent it so that the interpreter can easily execute the Python code.
Indentation is applied on conditional statements and loop control statements. Indent specifies the block of code that is to be executed depending on the conditions.
Conditional Statements
 ⇧

The if, elif and else 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
example

a=15
b=20
c=12
if(a>b and a>c):
      print(a,"is greatest")
elif(b>c and b>a):
      print(b," is greatest")
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

else:
    print(c,"is greatest")


Loops in Python
 ⇧

A loop or iteration statement 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
example

for i in range(1,101,1):
           print(i)

 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
example

i=1
while(i<=100):
        print(i)
        i=i+1

 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
example

for i in range(1,101,1):
    print(i ,end=" ")
    if(i==50):
        break
    else:
        print("Mississippi")
print("Thank you")

            

 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
example

Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

for i in [2,3,4,6,8,0]:
    if (i%2!=0):
        continue
    print(i)
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():
          #statements
def keyword is used before defining the function. 

 Function Call
my_function()
Whenever we need that block of code in our program simply call that function name whenever neeeded. If parameters are passed during defing the function we have to pass the parameters while calling that function
example

def add():       #function defination
        a=10
        b=20
       print(a+b)
add()            #function call

 Return statement in Python function
The function return statement return the specified value or data item to the caller. 

return [value/expression]

 Arguments in python function
Arguments are the values passed inside the parenthesis of the function while defining as well as while calling.

def my_function(arg1,arg2,arg3....argn):
          #statements
my_function(arg1,arg2,arg3....argn)
example

Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

def add(a,b):
      return a+b
x=add(7,8)
print(x)
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", " mode")

 modes-

r - to read the content from file
w - to write the content into file
a - to append the existing content into file
r+:  To read and write data into the file. The previous data in the file will be overridden.
w+: To write and read data. It will override existing data.
a+: To append and read data from the file. It won’t override existing data.


 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

readlines() #returns a list
It returns one line at a time

readline #returns one line at a time

 write function
This function writes a sequence of strings to the file.

Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

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

writelines()
Exception Handling
 ⇧

An exception is an unusual condition that results in an interruption in the flow of a 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 Exceptionname:
    [Error processing block]

 else
The else block is executed if the try block have not raise any exception and code had been running successfully

try:
     #statements
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

except:
     #statements
else:
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

      #statements
finally
 ⇧

Finally block will be executed even if try block of code has been running successsfully or except block of code is been executed. finally block of code will be executed compulsory

Object Oriented Programming (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:
    pass #statements

 Creating an object
Instantiating an object can be done as follows:

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

 self parameter
The self parameter is the first parameter of any function present in the class. It can be of different name but this parameter is must while defining any function into class as it is used to access other data members of the class

 class with a constructor
Constructor is the special function of the class which is used to initialize the objects. The syntax for writing a class with the constructor in python

class CodeWithHarry:

    # Default constructor
    def __init__(self):
        self.name = "CodeWithHarry"

    # A method for printing data members
    def print_me(self):
        print(self.name)

 Inheritance in python
By using inheritance, we can create a class which uses all the properties and behavior of another class. The new class is known as a derived class or child class, and the one whose properties are acquired is known as a base class or parent class.
It provides the re-usability of the code.

class Base_class:
       pass
class derived_class(Base_class):
        pass

 Types of inheritance-
Single inheritance
Multiple inheritance
Multilevel inheritance
Hierarchical inheritance

 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
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

Used to find whether a class is a subclass of a given class or not as follows

issubclass(obj, classinfo) # returns true if obj is a subclass of classinfo

Iterators and Generators
 ⇧

An iterable is any Python object capable of returning its members one at a time, permitting it to be iterated over in a for-loop. 
Familiar examples of iterables include lists, tuples, and strings - any such sequence can be iterated over in a for-loop.

Here are some useful built-in functions that accept iterables as arguments:
list, tuple, dict, set: construct a list, tuple, dictionary, or set, respectively, from the contents of an iterable
sum: sum the contents of an iterable.
sorted: return a list of the sorted contents of an interable
any: returns True and ends the iteration immediately if bool(item) was True for any item in the iterable.
all: returns True only if bool(item) was True for all items in the iterable.
max: return the largest value in an iterable.
min: return the smallest value in an iterable.

Here are some of the advanced PythonCStopics 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')
Basics
Comments
Escape Sequence
Strings
List
Tuples
Sets
Dictionaries
Indentation
Conditional Statements
Loops in Python
Functions
File Handling
Exception Handling
finally
Object Oriented Programming (OOPS)
Iterators and Generators
Decorators

    yield n
    n += 1
    print('This is printed at last')
    yield n
Decorators
 ⇧

Decorators are used to modifying the behavior of a function or a 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