Python Cheat sheet for Beginners

Here is a beginners cheat sheet for Python programming language:

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Python Basics

Data Types

read Also-Python Data Types

Python has several data types including:

• Integers: Whole numbers, such as 1, 2, 3
• Floats: Decimal numbers, such as 1.0, 1.5, 3.14
• Booleans: True or False values
• Strings: A sequence of characters, such as “hello world”
• Lists: A collection of ordered elements, such as [1, 2, 3]
• Dictionaries: A collection of key-value pairs, such as {“name”: “John”, “age”: 30}
• Tuples: A collection of ordered, immutable elements, such as (1, 2, 3)

Variables

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In Python, variables can be assigned values using the = operator. For example:

codex = 5
y = "hello"

Printing Output

To print output in Python, use the print() function. For example:

print("hello world")

Arithmetic Operators

Read more-Python Operators

Python supports common arithmetic operators, including:

• + addition
• - subtraction
• * multiplication
• / division
• // floor division
• % modulus
• ** exponentiation

Comparison Operators

Python supports common comparison operators, including:

• == equal to
• != not equal to
• < less than
• > greater than
• <= less than or equal to
• >= greater than or equal to

Logical Operators

Python supports common logical operators, including:

• and logical AND
• or logical OR
• not logical NOT

Conditional Statements

Python supports if-else statements for conditional execution of code. For example:

if x > 10:
    print("x is greater than 10")
else:
    print("x is less than or equal to 10")

Loops

Python supports for and while loops for iterating over collections and executing code repeatedly. For example:

for i in range(10):
    print(i)
    
while x < 10:
    print(x)
    x += 1

Functions

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Defining Functions

Functions can be defined in Python using the def keyword. For example:

def square(x):
    return x * x

Calling Functions

Functions can be called in Python by passing arguments to them. For example:

result = square(5)
print(result) # prints 25

File I/O

Opening Files

Files can be opened in Python using the open() function. For example:

file = open("example.txt", "r")

Reading Files

Files can be read in Python using the read() method. For example:

content = file.read()
print(content)

Writing to Files

Files can be written to in Python using the write() method. For example:

file = open("example.txt", "w")
file.write("Hello world")
file.close()

Libraries

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Importing Libraries

Libraries can be imported in Python using the import keyword. For example:

import math

Using Libraries

Libraries can be used in Python by calling their functions. For example:

result = math.sqrt(16)
print(result) # prints 4.0

Lists

Creating Lists

Lists can be created in Python using square brackets []. For example:my_list = [1, 2, 3]

Accessing List Elements

List elements can be accessed using indexing, starting from 0. For example

print(my_list[0]) # prints 1

Modifying List Elements

List elements can be modified by assigning new values to them. For example:

my_list[0] = 4 
print(my_list) # prints [4, 2, 3]

List Methods

Python provides many useful methods for working with lists, such as:

• append(): adds an element to the end of the list
• extend(): adds elements from another list to the end of the list
• insert(): adds an element at a specific position in the list
• remove(): removes the first occurrence of an element from the list
• pop(): removes and returns the element at a specific position in the list
• index(): returns the index of the first occurrence of an element in the list
• count(): returns the number of times an element appears in the list
• sort(): sorts the elements in the list
• reverse(): reverses the order of the elements in the list

Dictionaries

Creating Dictionaries

Dictionaries can be created in Python using curly braces {}. For example:

my_dict = {"name": "John", "age": 30}

Accessing Dictionary Elements

Dictionary elements can be accessed using keys. For example

print(my_dict["name"]) # prints "John"

Modifying Dictionary Elements

Dictionary elements can be modified by assigning new values to them. For example:

my_dict["age"] = 31 
print(my_dict) # prints {"name": "John", "age": 31}

Dictionary Methods

Python provides many useful methods for working with dictionaries, such as:

• keys(): returns a list of all the keys in the dictionary
• values(): returns a list of all the values in the dictionary
• items(): returns a list of all the key-value pairs in the dictionary
• get(): returns the value associated with a key, or a default value if the key is not found
• pop(): removes and returns the value associated with a key
• update(): updates the dictionary with key-value pairs from another dictionary

Classes

Creating Classes

Classes can be created in Python using the class keyword. For example:

class Person: def __init__(self, name, age): 
self.name = name self.age = age def greet(self): print("Hello, my name is", self.name)

Creating Objects

Objects can be created from classes using the class name and parentheses. For example:

person = Person("John", 30)

Accessing Object Attributes

Object attributes can be accessed using dot notation. For example:

print(person.name) # prints "John"

Calling Object Methods

Object methods can be called using dot notation and parentheses. For example

person.greet() # prints "Hello, my name is John"

That’s a quick overview of some of the basics of Python programming. There’s a lot more to learn, but this should give you a good starting point!

Control Flow

if-else Statements

The if-else statement is used to conditionally execute code based on a boolean expression. For example

if x > 0: 
print("x is positive")
 else: 
print("x is not positive")

for Loops

The for loop is used to iterate over a sequence of elements. For example

for i in range(5): 
print(i)

while Loops

The while loop is used to repeatedly execute code while a boolean expression is true. For example:

i = 0
 while i < 5: 
print(i)
 i += 1

break and continue Statements

The break statement is used to exit a loop prematurely, while the continue statement is used to skip over an iteration of a loop. For example:

for i in range(10):
 if i == 5:
 break
 if i % 2 == 0: 
continue 
print(i)

Functions in Python for Beginners

Beginners can understood the basics of functions by the following topics:

Defining Functions

Functions are defined in Python using the def keyword. For example:

def square(x):
 return x * x

Calling Functions

Functions are called by their name followed by parentheses, with any arguments passed inside the parentheses. For example

print(square(3)) # prints 9

Default Arguments

Functions can have default argument values, which are used if an argument is not provided. For example:

def greet(name="World"): 
print("Hello,", name)
 greet() # prints "Hello, World" greet("John") # prints "Hello, John"

Variable Arguments

Functions can accept a variable number of arguments using the *args syntax. For example:

def add(*args): 
result = 0
 for arg in args:
 result += arg
 return result
 print(add(1, 2, 3)) # prints 6

Modules

Importing Modules

Modules can be imported in Python using the import keyword. For example

import math 
print(math.sqrt(4)) # prints 2.0

Alias Modules

Modules can be aliased using the as keyword. For example

import math as m 
print(m.sqrt(4)) # prints 2.0

Importing Functions from Modules

Individual functions can be imported from modules using the from ... import ... syntax. For example:

from math import sqrt 
print(sqrt(4)) # prints 2.0

Data Structures

Lists

Lists are a sequence of elements that can be accessed by their index. For example:

fruits = ["apple", "banana", "cherry"] 
print(fruits[1]) # prints "banana"

Tuples

Tuples are like lists, but they are immutable, meaning that their values cannot be changed. For example:

point = (3, 4) 
print(point[0]) # prints 3

Dictionaries

Dictionaries are collections of key-value pairs, which can be accessed by their keys. For example:

person = {"name": "John", "age": 30} 
print(person["name"]) # prints "John"

Sets

Sets are collections of unique elements. For example:

fruits = {"apple", "banana", "cherry"} 
fruits.add("apple") 
print(fruits) # prints {"apple", "banana", "cherry"}

Object-Oriented Programming for beginners

OOP in Python for beginners are simply understood by following topics:

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Classes

Classes define objects with shared properties and methods. For example:

class Person:
 def __init__(self, name, age):
 self.name = name
 self.age = age
def greet(self):
 print("Hello, my name is", self.name) person = Person("John", 30)
 person.greet() # prints "Hello, my name is John"

Inheritance

Inheritance allows classes to inherit properties and methods from parent classes. For example

class Student(Person):
 def __init__(self, name, age, major): super().__init__(name, age) self.major = major def greet(self): super().greet()
 print("I am studying", self.major) 
student = Student("Jane", 20, "Computer Science") 
student.greet() # prints "Hello, my name is Jane" followed by "I am studying Computer Science"

File Input/Output

Opening Files

Files can be opened using the open function. For example:

file = open("example.txt", "r")

Reading Files

Files can be read using the read function. For example

contents = file.read()

Writing to Files

Files can be written to using the write function. For example

file.write("Hello, World!")

Closing Files

Files should be closed using the close function. For example:

file.close()

That’s a quick overview of some of the more advanced features of Python for beginners. With these tools in your toolkit, you’ll be able to write powerful and flexible programs in Python!

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