Learn Python 001

Note: I’m not an expert. I’m writing this blog just to document my learning journey. 🚀

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1. What is Python?

Python is a tool we use to give instructions to a computer.
It’s a programming language — a way to write tasks in simple, readable English-like words so the computer can follow them.

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2. What is a Program?

A program is a list of instructions that a computer runs step by step.

To write a program in Python, we write instructions using Python’s rules (called syntax). The instructions tell the computer what to do with data (numbers, text, etc.).

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3. What is Data?

Data is information — like:

• Numbers (10)
• Text ("hello")
• True/False values (True, False)

Every piece of data has a type. Common types in Python:

• int: whole numbers like 5
• float: decimal numbers like 3.14
• str: text like "Python"
• bool: truth values: True or False

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4. What are Variables?

A variable is a name you give to a piece of data so you can use it later.

age = 25
name = "Alice"

Here, age stores the number 25, and name stores the word "Alice".

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5. What Can You Do With Data?

You use operators to do things with data.

Math:

5 + 2   # 7
5 - 2   # 3
5 * 2   # 10
5 / 2   # 2.5

Comparisons:

5 > 2      # True
3 == 3     # True
4 != 5     # True

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6. How to Make Decisions in Code

We use if statements to tell Python: “Only do this if a condition is true.”

age = 18

if age >= 18:
    print("You are an adult")
else:
    print("You are a minor")

Python checks the condition. If it's true, it runs the code under if. Otherwise, it runs the code under else.

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7. How to Repeat Things

You use loops to repeat actions.

for loop – repeats a set number of times:

for i in range(3):
    print("Hello")

This prints "Hello" three times.

while loop – repeats while a condition is true:

count = 0
while count < 3:
    print(count)
    count += 1

This prints 0, 1, and 2.

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8. Functions: Reusable Code

A function is a block of code that does one job. You can run it (call it) whenever you want.

def greet(name):
    print("Hello", name)

greet("Alice")

You define it with def, give it a name, and call it by writing its name and giving it any needed inputs.

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9. Lists: A Collection of Values

A list holds multiple values in one variable.

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

You can get items by position:

print(fruits[0])  # apple

You can also add to it:

fruits.append("orange")

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10. Dictionaries: Key-Value Pairs

A dictionary stores values with names (keys), like a mini-database.

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

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11. Handling Errors

Sometimes code breaks. You can handle errors using try and except.

try:
    print(10 / 0)
except ZeroDivisionError:
    print("Can't divide by zero")

This stops the program from crashing.

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12. Using Tools: Importing Modules

Python has extra features stored in modules. You can bring them into your code using import.

import math
print(math.sqrt(16))  # 4.0

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13. Classes and Objects: Building Custom Types

A class is like a blueprint. It defines what something is and what it can do.
An object is a thing made from that blueprint.

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

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

my_dog = Dog("Buddy")
my_dog.bark()  # Buddy says woof!

You use classes to organize your code and model real things.

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Summary

Python lets you:

• Store data in variables
• Use operators to work with data
• Make decisions with if
• Repeat tasks with loops
• Reuse code with functions
• Group data with lists and dictionaries
• Handle errors
• Use built-in tools (modules)
• Build custom structures with classes

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