📦 1. Functions with Return Values
A function is like a machine. You give it input, it gives you output.
# This function takes two numbers and returns their sum
def add_numbers(a, b):
result = a + b
return result # sends the result back to the caller
# Calling the function and storing the output
total = add_numbers(5, 3)
print("The total is:", total)
💡 Explanation:
def means you're defining a function.
return gives the result back to the place it was called from.
You can call this function anytime to add numbers.
🧱 2. Default Parameters in Functions
def greet(name="friend"):
print("Hello", name)
greet("Arvind") # Hello Arvind
greet() # Hello friend (default value is used)
💡 Explanation:
If the user doesn’t provide a name, it uses "friend".
🧠 3. Dictionaries (key-value pairs)
Dictionaries are used to store data in pairs (like a mini database).
student = {
"name": "Arvind",
"age": 25,
"grade": "A"
}
# Accessing values
print(student["name"]) # Arvind
print(student.get("age")) # 25
# Adding a new key
student["passed"] = True
# Looping through keys and values
for key, value in student.items():
print(key, ":", value)
💡 Explanation:
{} defines a dictionary.
You can get values using keys, e.g., student["name"].
.items() gives both key and value in a loop.
🔁 4. Looping with Index – Using enumerate()
colors = ["red", "blue", "green"]
for index, color in enumerate(colors):
print("Index:", index, "→ Color:", color)
💡 Explanation:
enumerate() gives both index and item.
Helps when you need the position of each item in a list.
🚫 5. Error Handling (try-except)
Sometimes your code may fail (e.g., dividing by 0). You can handle it:
try:
number = int(input("Enter a number: "))
result = 10 / number
print("Result:", result)
except ZeroDivisionError:
print("You can't divide by zero.")
except ValueError:
print("That wasn't a valid number.")
💡 Explanation:
try: Try running the code.
except: If error happens, catch and handle it.
This prevents your program from crashing.
🔃 6. Nested Loops
When you need a loop inside another loop (e.g., printing patterns):
for i in range(1, 4): # Outer loop
for j in range(1, 4): # Inner loop
print(f"({i}, {j})", end=" ")
print() # for a new line
💡 Output:
(1, 1) (1, 2) (1, 3)
(2, 1) (2, 2) (2, 3)
(3, 1) (3, 2) (3, 3)
🔄 7. Using range() with Loops
# Print numbers 0 to 4
for i in range(5):
print(i)
# Print 1 to 10
for i in range(1, 11):
print(i)
# Print every 2nd number from 2 to 10
for i in range(2, 11, 2):
print(i)
💡 Explanation:
range(start, end, step)
Python’s range() is very useful for loops.
✅ Quick Review
Concept Explanation
return- Sends back result from a function
Dictionary -Key-value storage
try-except -Handle errors safely
enumerate()- Loop with index
range() -Create number sequences
Nested loops- Loops inside loops
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