Home / Python / Day 5: Files & Error Handling / Try / Except

Try / Except

Handle errors gracefully with try-except blocks.

Exception Handling

Exceptions are errors that occur during program execution. Python's try-except lets you catch and handle these errors gracefully.

Syntax

<pre><code># Basic try-except
try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

# Multiple exceptions
try:
    num = int(input("Enter a number: "))
    result = 100 / num
except ValueError:
    print("Not a valid number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")
except Exception as e:
    print(f"Unexpected error: {e}")
else:
    print(f"Result: {result}")  # Runs if no exception
finally:
    print("Always runs")         # Always executes

# Custom exceptions
class InsufficientFundsError(Exception):
    def __init__(self, amount, balance):
        super().__init__(f"Cannot withdraw {amount}, balance is {balance}")

# Raising exceptions
def withdraw(balance, amount):
    if amount > balance:
        raise InsufficientFundsError(amount, balance)
    return balance - amount
</code></pre>

Revision Notes

• try: risky code; except: handle error
• else: runs if no exception; finally: always runs
• Catch specific exceptions before general Exception
• raise to throw an exception
• Custom exceptions extend Exception class

Safe Division with Exceptions

Easy

Write a function safe_divide(a, b) that returns a divided by b. If b is zero, return the string "Cannot divide by zero" instead of raising an error. If either input is not a number, return "Invalid input". Use try/except.

Input:

safe_divide(10, 2), safe_divide(5, 0), safe_divide(5, "x")

Output:

5.0 Cannot divide by zero Invalid input

Show Hint

Use try/except catching ZeroDivisionError and TypeError separately.

Solve this Challenge

Show Solution

def safe_divide(a, b):
    try:
        return a / b
    except ZeroDivisionError:
        return "Cannot divide by zero"
    except TypeError:
        return "Invalid input"

print(safe_divide(10, 2))
print(safe_divide(5, 0))
print(safe_divide(5, "x"))

File Handling Back to Course