1. Basic try/except

Instead of letting errors crash your program, you can catch them and handle them gracefully:

age = input("Enter your age: ")  # User types "twenty"
age = int(age)    # ValueError! Program crashes
print(f"You are {age} years old")

try:
    age = input("Enter your age: ")
    age = int(age)
    print(f"You are {age} years old")
except:
    print("Please enter a valid number.")

2. Catching Specific Exceptions

It is best practice to catch specific exception types rather than catching everything:

try:
    number = int(input("Enter a number: "))
    result = 100 / number
    print(f"100 / {number} = {result}")
except ValueError:
    print("That's not a valid number!")
except ZeroDivisionError:
    print("You can't divide by zero!")

try:
    file = open("missing.txt", "r")
except FileNotFoundError as e:
    print(f"Error: {e}")

3. The else Clause

The else block runs only if no error occurred in the try block:

try:
    number = int(input("Enter a number: "))
except ValueError:
    print("Invalid input!")
else:
    # Only runs if no error occurred
    print(f"You entered: {number}")
    print(f"Doubled: {number * 2}")

4. The finally Clause

The finally block runs no matter what - whether an error occurred or not. It is useful for cleanup tasks:

try:
    file = open("data.txt", "r")
    content = file.read()
    print(content)
except FileNotFoundError:
    print("File not found!")
finally:
    print("Finished file operation.")
    # This always runs

try:
    value = int(input("Enter a number: "))
except ValueError:
    print("Not a valid number!")
else:
    print(f"Success! You entered {value}")
finally:
    print("Program complete.")

# Order: try → except (if error) OR else (if no error) → finally (always)

5. Raising Exceptions

You can raise your own exceptions using the raise keyword:

def set_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative")
    if age > 150:
        raise ValueError("Age seems unrealistic")
    return age

try:
    my_age = set_age(-5)
except ValueError as e:
    print(f"Invalid age: {e}")

6. Practical Example: Safe User Input

def get_positive_number():
    while True:
        try:
            num = float(input("Enter a positive number: "))
            if num <= 0:
                print("Number must be positive!")
            else:
                return num
        except ValueError:
            print("That's not a valid number. Try again.")

result = get_positive_number()
print(f"You entered: {result}")