📂 Python Basics Cheatsheet

🐍 Python Basics Cheatsheet

🚀 Master the essentials of Python – your gateway to automation, web dev, data science, and beyond.

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🧠 Python Syntax Overview

# This is a comment
# (Think of this like a note for humans, Python ignores it)

print("Hello, world!")  # Output something to the screen
# This shows the words “Hello, world!” on your screen

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🔢 Variables and Data Types

Variables are like boxes where you can store stuff — numbers, words, or True/False.

# Numbers
x = 10          # x is a box that holds the number 10 (integer)
pi = 3.14       # pi holds a decimal number (called a float)

# Strings (words inside quotes)
name = "Sri"    # name holds the word Sri
greeting = 'Hello'  # greeting holds Hello (single or double quotes both work)

# Booleans (True or False — like Yes or No)
is_coding = True     # means YES, I am coding
is_sleeping = False  # means NO, I am not sleeping

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🎯 Input and Output

Input lets you ask the user something. Output shows something on the screen.

name = input("What's your name? ")
# This asks the user their name and saves it into a box called 'name'

print("Hello", name)
# This shows: Hello <whatever the user typed>

🧸 Example:

What's your name? → Sri  
Output: Hello Sri

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🧮 Operators

Operators help us do things like math, comparisons, and logic.

# Arithmetic Operators (like in school)
+  # Add things
-  # Subtract
*  # Multiply
/  # Divide
%  # Remainder after division
** # Power (2 ** 3 means 2 to the power of 3 = 8)
// # Floor divide (cuts off decimals)

# Comparison Operators
==  # Is equal to?
!=  # Is NOT equal?
>   # Greater than?
<   # Less than?
>=  # Greater than or equal to?
<=  # Less than or equal to?

# Logical Operators
and  # Both conditions must be True
or   # At least one must be True
not  # Opposite of the condition

🧸 Example:

2 + 3 == 5  # True
5 > 3 and 2 < 4  # True
not True  # False

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🔁 Control Flow

Control flow means making decisions and repeating stuff.

✅ Conditional Statements:

if x > 0:
    print("Positive")
elif x == 0:
    print("Zero")
else:
    print("Negative")

🧸 Example: If x = 5, it prints “Positive”.
If x = 0, it prints “Zero”.

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🔄 Loops:

Loops repeat things over and over.

# For loop: Repeat a fixed number of times
for i in range(5):
    print(i)

🧸 Output:

0
1
2
3
4

# While loop: Keep going until something is False
count = 0
while count < 5:
    print(count)
    count += 1  # Adds 1 each time

🧸 Output:

0
1
2
3
4

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📦 Functions

Functions are like mini-machines. You give them input, they give you output.

def greet(name):
    return "Hello " + name

message = greet("Sri")
print(message)

🧸 Output:

Hello Sri

Explanation:

• def greet(name): creates a function named greet
• return gives back the result
• You can reuse the function as many times as you want!

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📚 Lists and Loops

Lists are like toy boxes that hold multiple items.

fruits = ["apple", "banana", "cherry"]
# A list of 3 fruits

for fruit in fruits:
    print(fruit)  # Print each fruit one by one

🧸 Output:

apple
banana
cherry

fruits.append("mango")  # Add mango to the list

print(fruits[0])  # Shows the first fruit: apple

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🧰 Common Built-in Functions

Python has lots of ready-made tools (functions) you can use:

len("hello")      # Gives 5 (the number of letters)
type(10)          # Says it's an int (number)
int("5")          # Turns the string "5" into a number
str(10)           # Turns number 10 into a string
float("3.14")     # Makes it a decimal number
bool("")          # Empty things are False, others are True
range(3)          # Makes numbers 0, 1, 2

🧸 Example:

list(range(3)) → [0, 1, 2]

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💡 Tips

• Use snake_case for variable and function names (like: total_score, get_input)
• Indentation (spacing) is VERY important! Always use 4 spaces.
• To run your Python file:

  python filename.py

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📂 Python Data Structures Cheatsheet

🧱 Python Data Structures Cheatsheet

🎯 Data structures let you store, access, and organize your stuff (like toys, lists, or cards).
They help you remember things, find them fast, and keep them tidy when you're coding!

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🧺 1. Lists (A basket that holds items in order — and you can change them!)

fruits = ["apple", "banana", "mango"]

🧸 This is a list — like a toy basket.
It has three fruits, and you can do lots of things with it:

fruits.append("orange")     # Adds "orange" to the basket
fruits.remove("banana")     # Takes "banana" out
fruits[0]                   # Gets the first fruit ("apple")
fruits[1] = "grape"         # Changes second fruit to "grape"
len(fruits)                 # Counts how many fruits are in the basket

🔁 Loop through list (Look at each item one by one)

for fruit in fruits:
    print(fruit)

🧸 This prints each fruit one by one like:

apple  
grape  
mango  
orange  

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📚 2. Tuples (A list you can't change — like a locked box)

coordinates = (10, 20)
print(coordinates[0])     # Gets the first number (10)

🧸 Tuples are like coordinates on a map.
You can look at them, but you can't change them.

🔒 Use tuples when your data should stay the same.
Example: (latitude, longitude), or sizes like (width, height)

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🗃️ 3. Dictionaries (A label-sticker box: each item has a name and a value)

person = {"name": "Sri", "age": 17}

🧸 This is a dictionary. It’s like a box where each item has a label:

print(person["name"])        # Shows "Sri"
person["age"] = 18           # Changes age to 18
person["city"] = "Chennai"   # Adds a new label: "city"

🔁 Loop through dictionary (Check all labels and values)

for key, value in person.items():
    print(key, value)

🧸 Output:

name Sri  
age 18  
city Chennai

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🔢 4. Sets (A magic bag with only unique things – no duplicates allowed!)

numbers = {1, 2, 3, 2, 1}

🧸 This bag only keeps one of each number, so it becomes:

{1, 2, 3}

numbers.add(4)        # Adds number 4
numbers.remove(2)     # Removes number 2

👀 You can also check if something’s in the set:

if 3 in numbers:
    print("Found")

🧸 Output:

Found

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📊 Summary Table

Type	Ordered	Can Change?	Allows Duplicates?	Example
List	✅ Yes	✅ Yes	✅ Yes	["a", "b", "c"]
Tuple	✅ Yes	❌ No	✅ Yes	(1, 2, 3)
Dictionary	✅ Yes (by key)	✅ Yes	❌ No (keys must be unique)	{"key": "value"}
Set	❌ No	✅ Yes	❌ No	{1, 2, 3}

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🧠 Pro Tips

• ✅ Use lists when you need an ordered group of things you want to change
• 🔒 Use tuples when the data should never change
• 🏷️ Use dictionaries when each value needs a name or label
• 🧹 Use sets to remove duplicates or check if something exists

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📂 Python OOP Cheatsheet

🧱 Python OOP (Object-Oriented Programming) Cheatsheet

🧠 OOP lets you create your own blueprints for real things (like people, animals, cars).
It helps you organize your code and reuse it like LEGO blocks! 🧱

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🧬 1. What is a Class?

A class is like a blueprint or recipe.

class Dog:
    pass

🧸 Imagine you’re drawing a “Dog” template — but you haven’t made a real dog yet.

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🐾 2. What is an Object?

An object is a real thing made from a class.

my_dog = Dog()

Now you’ve made an actual dog using the Dog blueprint.
You can make as many dogs as you want!

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🎒 3. Attributes (What an object has)

class Dog:
    def __init__(self, name, age):
        self.name = name    # Every dog has a name
        self.age = age      # Every dog has an age

Explanation:

• __init__() is a special function that runs when we create a new object
• self is the object itself (think: “this dog”)
• self.name and self.age are like labels on that specific dog

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🎯 4. Creating an Object (Using the class)

dog1 = Dog("Bruno", 3)
print(dog1.name)  # Bruno
print(dog1.age)   # 3

Now Bruno is your first dog. You can make more dogs too!

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⚙️ 5. Methods (What an object can do)

class Dog:
    def __init__(self, name):
        self.name = name

    def bark(self):
        print(self.name + " says woof!")

Now every dog can bark!

dog1 = Dog("Shadow")
dog1.bark()

🧸 Output:

Shadow says woof!

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👪 6. Inheritance (Like getting traits from your parents!)

class Animal:
    def eat(self):
        print("This animal eats food.")

class Cat(Animal):
    def meow(self):
        print("Meow!")

Now Cat can do everything Animal can do + its own stuff!

kitty = Cat()
kitty.eat()   # From Animal
kitty.meow()  # From Cat

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🧱 7. Encapsulation (Keep details private!)

class BankAccount:
    def __init__(self, balance):
        self.__balance = balance  # private!

    def deposit(self, amount):
        self.__balance += amount

    def get_balance(self):
        return self.__balance

The __balance is private. You can't access it directly!

account = BankAccount(1000)
account.deposit(500)
print(account.get_balance())  # 1500

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🔁 8. Polymorphism (Same word, different behavior)

class Bird:
    def speak(self):
        print("Chirp!")

class Duck(Bird):
    def speak(self):
        print("Quack!")

class Parrot(Bird):
    def speak(self):
        print("Squawk!")

Now each bird has its own voice:

for bird in [Duck(), Parrot(), Bird()]:
    bird.speak()

🧸 Output:

Quack!  
Squawk!  
Chirp!

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🧠 Summary Table

Concept	What it Means (Kid Version)	Python Example
Class	A blueprint for things	class Dog:
Object	A real thing made from a class	dog1 = Dog()
Attribute	Something an object has	self.name
Method	Something an object does	def bark(self):
Inheritance	Child inherits from parent	class Cat(Animal):
Encapsulation	Hide secret stuff inside a box	self.__balance
Polymorphism	Same method, different behaviors	def speak() in many classes

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💡 Pro Tips for OOP

• Use PascalCase for class names (class MyCar)
• Always use self inside classes — it refers to the object
• OOP is great for games, web apps, cybersecurity tools, and everything real-world

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🎮 Think of classes as characters, attributes as stats, and methods as powers.
Master OOP and you’ll code like a dev boss 💻👑

📂 File Handling + Modules & Packages Cheatsheet

🐍 Python Scrolls — File Handling + Modules & Packages (Beginner Ninja Guide)

Welcome, apprentice! In this scroll, you’ll learn how to open files, write into them, and reuse code using modules & packages. Everything is explained simply, with examples. Let's begin! 🧠

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📁 Python File Handling — Read, Write, Append Like a Pro!

Think of a file like a notebook on your computer. You can open it, read what's inside, write something new, or add more stuff at the end.

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📖 How to Open and Read a File

file = open("example.txt", "r")  # "r" means read mode
content = file.read()            # Reads everything in the file
print(content)                   # Shows it on the screen
file.close()                     # Closes the file

🧸 Imagine opening your storybook, reading it, and then closing it.

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✍️ How to Write to a File

file = open("example.txt", "w")  # "w" means write mode (starts fresh)
file.write("Hello, world!")      # Writes this sentence inside the file
file.close()                     # Close the book after writing

📌 "w" deletes everything and starts clean like a new notebook.

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➕ How to Add More (Append)

file = open("example.txt", "a")     # "a" means append (add)
file.write("\nNew line added!")     # Adds new text on a new line
file.close()

📌 "a" is like turning to the next page and continuing the story.

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🧼 Best Practice — Use with (Auto-Close)

with open("example.txt", "r") as file:  # Open and name it 'file'
    content = file.read()               # Read the content
    print(content)                      # Print it out

✅ Using with makes sure your file is always closed — even if there's an error.

with open("example.txt", "w") as file:
    file.write("Safe writing with context manager")

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🔁 Read File Line by Line

with open("example.txt", "r") as file:
    for line in file:              # Go through each line one by one
        print(line.strip())        # Print each line, but remove the '\n' newline

📌 strip() removes invisible characters like extra spaces or newlines.

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📋 File Modes Cheat Table

Mode	What It Means	Example
"r"	Read only	open("file.txt", "r")
"w"	Write (erase)	open("file.txt", "w")
"a"	Append	open("file.txt", "a")
"x"	Create new	open("file.txt", "x")
"b"	Binary	open("file.png", "rb")

🤖 Combine them like "rb" (read in binary) or "wb" (write in binary)

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🧠 File Handling Tips

• Always use with open(...) → safer and cleaner!
• Use "a" to add stuff, "w" to overwrite, "r" to read.
• Use .strip() to clean up text.
• You can also use os and pathlib for pro-level file tasks.

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📦 Python Modules & Packages — Code Reusability Superpower

Imagine breaking your huge project into smaller magic scrolls (modules) and storing them inside chests (packages). Let’s learn how!

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📁 What Is a Module?

A module is just a .py file that has code you want to reuse.

🧪 Example:

# math is a built-in module
import math
print(math.sqrt(16))  # ➜ 4.0

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🎲 Random Module Example

import random
print(random.randint(1, 10))  # ➜ a number between 1 to 10

🎉 Now your app can roll virtual dice!

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🎯 Use from ... import to Be More Specific

from math import sqrt, pi
print(sqrt(25))  # ➜ 5.0
print(pi)        # ➜ 3.141592...

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from random import choice
print(choice(["Sri", "Dukkie", "Ninja"]))  # Picks one name randomly

🧠 from lets you import only what you need.

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🧰 Make Your Own Module

File: my_module.py

def greet(name):
    return f"Hello, {name}!"

Another file: main.py

import my_module
print(my_module.greet("Sri"))  # ➜ Hello, Sri!

🧙 You just created and used your own magic scroll!

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📦 What is a Package?

A package is a folder with multiple modules and a special file called __init__.py

my_package/
│
├── __init__.py
├── module1.py
└── module2.py

📦 Use a Module from a Package

from my_package import module1
module1.function_name()

🎒 Packages help organize related modules.

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🔍 Built-in vs External Modules

Type	Example	How to Use
Built-in	math, os	Comes with Python
External	flask, requests	Install with pip

pip install requests

🧰 External modules = advanced tools from Python community

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🧠 Pro Tools — Explore Like a Curious Kid

import math
print(dir(math))       # ➜ Shows all math functions
print(help(math.sqrt)) # ➜ Explains what sqrt does

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🧠 Module & Package Tips

• Break code into smaller .py files
• Use import to reuse code again and again
• Group related modules inside packages
• Use pip to install amazing external tools

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🎉 You’ve Mastered:

✅ Reading, writing & appending to files
✅ Creating & importing modules
✅ Using Python packages
✅ Installing external tools with pip

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👑 Now you're not just a coder... you're a Python Scrollkeeper 🐍📜
Let me know what scroll to unlock next!