25 Jul Python Cheat Sheet

The Python Cheat Sheet will guide you to work on Python with basics and advanced topics. Cheat Sheet for students, engineers, and professionals.

Introduction

Python is a powerful, interpreted, object-oriented programming language. It is used in many areas for development and is considered a perfect language for scripting.

Features of Python

• Cross-platform
• Open Source
• Multiple Programming-paradigms
• Fewer lines of code
• Powerful Libraries

Install and Run Python

Python can be easily installed on any OS. You can also use any of the below platforms to run Python:

• Install Python on Windows
• Run Python on VS Code
• Run Python on Google Colab
• Run Python on Anaconda
• Run Python on PyCharm IDE Community Edition

Variables

Variables in Python are reserved memory locations. You only need to assign a value in Python, for variable declaration and that’s it!

Scope of Variables

The existence of a variable in a region is called its scope, or the accessibility of a variable defines its scope:

• Local Scope: Whenever a variable is defined in a function, it can be used only in that function.
• Global Scope: A variable has Global Scope, if it’s created outside the function i.e. the code body, and is accessible from anywhere.
• GLOBAL keyword: To change the value of a global variable inside the function, use the GLOBAL keyword

Tokens

Python Tokens are individual units in a program. The following are the types of Tokens:

• Keywords: Keywords are reserved words used in programming languages, for example, if, else, not, continue, return, try, etc.
• Identifiers: Identifiers in Python are used for naming variables, functions, and arrays. Do not use keywords as identifiers.
• Literals: Literals are the values assigned to each constant variable:
  • String Literals: Enclose the text in quotes. We can use both single as well as double quotes. Use triple quotes for multi-line strings.
  • Numeric Literals: Includes int, long, float, and complex.
  • Boolean Literals: Can have either True or False values

Operators

• if statement
  
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  if condition:     code will execute if condition is true;

• if-else statement
  
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  if condition:     code will execute if condition is true else:     code will execute if condition is false

• if…elif…else statement
  
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  if condition1:     code will execute if condition is true elif condition2:     code will execute if another condition is true elif condition3:     code will execute if above conditions aren’t true else:     code will execute if all the above given conditions are false

• break statement: The current loop is terminated and the execution of the program aborted. After termination, the control reaches the next line after the loop.
  
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  break;

• continue statement: The continue statement in Python transfers control to the conditional expression and jumps to the next iteration of the loop.
  
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  continue;

Loops

Loops execute a block of code and this code executes while the condition is true:

• while loop
  
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  while (condition is true):   code

• for loop
  
  
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  for var in sequence:   code

Numbers

To store Number types, such as integers, floats, etc., In Python3, Numbers include int, float, and complex datatypes,

Output

Strings

Strings in Python are sequences of characters that can be easily created:

• Create a String:
  
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  str = 'My name is Amit!'

• Slicing to access substrings:
  
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  str[7:10]

• Accessing a character:
  
  
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  str[9]

• Concatenate Strings:
  
  
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  str1 + str2

• String Operators:

Functions

A function in Python is an organized block of reusable code, that avoids repeating the tasks. Functions in Python begin with the keyword def and are followed by the function name and parentheses.

• Create a Function:
  
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  def function_name( parameters ):     function_suite     return [expression]

• Function Parameters:
  
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  def function_name(parameter1, parameter2, … ):

Lambda Functions

A lambda function is a function without a name i.e. an anonymous function. The keyword lambda is used to define a lambda function in Python and has only a single expression.

Multiply a number by an argument with lambda:

Classes & Objects

A class is the basis of object-oriented programming in Python. A class is a template for an object, whereas an object is an instance of a class. Example of a Class:

Example of Objects:

Output

Tuples

Tuple is a sequence in Python, a collection of objects. Also, Python Tuples are immutable i.e. you cannot update a tuple or any of its elements.

• Create a Tuple with string elements:
  
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  mytuple = ("Amit", "Craig", "Ronaldo", "Messi")

• Create a Tuple with int elements:
  
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  mytuple2 = (10, 20, 50, 100)

• Access values in a Tuple:
  
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  #First item mytuple[0] #Second item mytuple[1]

• Fetch a specific element with indexing in Tuples:
  
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  Fetch a specific element at 1st position: mytuple[0] Fetch a specific element at 2nd position: mytuple[1] Fetch a specific element at 3rd position: mytuple[2] Fetch a specific element at 4th position: mytuple[3]

• Length of Tuple:
  
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  len(mytuple)

• Get the maximum value from a Tuple:
  
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  max(mytuple)

• Get the minimum value from a Tuple:
  
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  min(mytuple)

Dictionary

The dictionary represents the key-value pair in Python, enclosed in curly braces. Keys are unique and a colon separates them from value, whereas a comma separates the items.

• Create a Dictionary:
  
  
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  mystock = {"Product": "Earphone", "Price": 800, "Quantity": 50}

  
  
• Access values in a Dictionary:
  
  
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  mystock["Product"]

• Print all the keys of a Dictionary:
  
  
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  mystock.keys()

• Print all the values of a Dictionary:
  
  
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  mystock.values()

• Get the length of a Dictionary:
  
  
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  len(mystock)

Lists

Lists in Python are ordered. It is modifiable and changeable, unlike Tuples.

• Create a List with int elements:
  
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  mylist = [25, 50, 75, 100, 125, 150, 175, 200 ];

• Create a List with string elements:
  
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  mylist = ["Nathan", "Darren", "Blair", "Bryce", "Stacey" ];

• Access values from a List:
  
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  print(mylist[2])

• Indexing in Lists:
  
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  Fetch a specific element at 1st position: mylist[0] Fetch a specific element at 2nd position: mylist[1] Fetch a specific element at 3rd position: mylist[2] Fetch a specific element at 4th position: mylist[3]

• Get the length of a List:
  
  
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  len(mylist)

• Get the maximum from a List:
  
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  max(mylist)

• Get the minimum from a List:
  
  
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  min(mylist)

Sets

A Set is a collection in Python. Set items i.e. elements are placed inside curly braces {}:

• Create a Set with int elements
  
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  myset = {"amit", "john", "kane", "warner", "steve"}

• Create a Set with string elements
  
  
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  myset2 = {5, 10, 15, 20, 25, 30}

• Get the length of a Set
  
  
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  len(myset)

• Return the difference between the two sets:
  
  
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  res = myset1.difference(myset2)

• Keep only the duplicate items in the two sets:
  
  
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  myset1.intersection_update(myset2)

• Keep all the items in the two sets except the duplicates:
  
  
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  myset1.symmetric_difference_update(myset2)

• Union of Sets
  
  
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  res = myset1.union(myset2)

Modules

The modules in Python are used to organize the code. We can easily import a module in Python using the import statement:

Example:

Here are the types of modules:

• math: The math module in Python is used to perform mathematical tasks, with functions, including, trigonometric, logarithmic, etc:
  
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  import math

• statistics:
  The statistics module in Python is used to perform statistical tasks, with statistical functions, including, mean, median, mode, stdev(), etc.
  
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  import statistics

• random
  The random module in Python is used to form random numbers. Here, we will see how to import a random module in a Python program.
  
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  import random

Learn Python via video course (English)

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What next?

• Python NumPy Tutorial
• Python Pandas Tutorial
• Python Matplotlib Tutorial
• Python Libraries Tutorial

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