Python Basics — A Practical Introduction to Python 3

Variables & Data Types

# No type declaration needed
name = "Rahul"        # str
age = 20              # int
height = 5.8          # float
is_student = True     # bool

# Check type
print(type(name))     # <class 'str'>
print(type(age))      # <class 'int'>

# Type conversion
num = int("42")       # str → int
text = str(100)       # int → str
decimal = float("3.14") # str → float

Strings

name = "Python"

# Methods
print(name.upper())      # PYTHON
print(name.lower())      # python
print(name[0])           # P (indexing)
print(name[1:4])         # yth (slicing)
print(len(name))         # 6
print(name.replace("P","J"))  # Jython

# f-strings (formatting)
age = 20
print(f"I am {age} years old")
print(f"Next year: {age + 1}")

Lists

fruits = ["Mango", "Apple", "Banana"]

print(fruits[0])         # Mango
print(fruits[-1])        # Banana
fruits.append("Grapes")  # Add item
fruits.remove("Apple")   # Remove item
print(len(fruits))       # 3

# List comprehension
squares = [x**2 for x in range(1,6)]
print(squares)  # [1, 4, 9, 16, 25]

If / Else

age = 18

if age >= 18:
    print("Adult")
elif age >= 13:
    print("Teenager")
else:
    print("Child")

# One-liner
status = "Adult" if age >= 18 else "Minor"
print(status)  # Adult

Loops

# For loop
for i in range(1, 6):
    print(i)  # 1 2 3 4 5

# Loop through list
for fruit in ["Mango", "Apple"]:
    print(fruit)

# While loop
count = 0
while count < 3:
    print(count)
    count += 1  # 0 1 2

# Print 1 to 10
print(*range(1, 11))

Functions

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

print(greet("Rahul"))  # Hello, Rahul!

# Default parameter
def add(a, b=10):
    return a + b

print(add(5))     # 15
print(add(5, 20)) # 25

# Lambda
square = lambda x: x**2
print(square(4))  # 16

Dictionaries

student = {
    "name": "Rahul",
    "age": 20,
    "marks": 85
}

print(student["name"])    # Rahul
student["city"] = "Pune"  # Add key

# Loop
for key, val in student.items():
    print(f"{key}: {val}")

File Handling

# Write
with open("data.txt", "w") as f:
    f.write("Hello Python!")

# Read
with open("data.txt", "r") as f:
    content = f.read()
    print(content)  # Hello Python!

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