Exception Handling in Python

Exception Handling in Python is used to handle runtime errors so that the normal flow of a program does not stop unexpectedly. It helps in writing robust, user-friendly, and error-free programs.

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What is an Exception?

An exception is an error that occurs during program execution. When an exception occurs, Python stops normal execution and raises an error.

Example (Without Exception Handling)

x = 10
y = 0
print(x / y)

Error: ZeroDivisionError

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Why Exception Handling is Important?

• Prevents program crash
• Handles unexpected user input
• Improves application reliability
• Provides meaningful error messages

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try and except Block

The try block contains code that may cause an exception, and the except block handles the exception.

try:
    x = 10
    y = 0
    print(x / y)
except ZeroDivisionError:
    print("Cannot divide by zero")

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Handling Multiple Exceptions

try:
    a = int("abc")
except ValueError:
    print("Invalid value")
except ZeroDivisionError:
    print("Division error")

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Using except as

You can capture the exception message using as.

try:
    x = int("abc")
except ValueError as e:
    print("Error:", e)

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try – except – else

The else block executes if no exception occurs.

try:
    num = int(input("Enter number: "))
except ValueError:
    print("Invalid input")
else:
    print("You entered:", num)

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try – except – finally

The finally block always executes, whether an exception occurs or not.

try:
    file = open("data.txt", "r")
except FileNotFoundError:
    print("File not found")
finally:
    print("Closing resources")

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Raising Exceptions (raise)

You can manually raise an exception using the raise keyword.

age = -5

if age < 0:
    raise ValueError("Age cannot be negative")

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User-Defined (Custom) Exceptions

Python allows you to create your own exceptions by extending the Exception class.

class InvalidAgeError(Exception):
    pass

try:
    age = 17
    if age < 18:
        raise InvalidAgeError("Not eligible to vote")
except InvalidAgeError as e:
    print(e)

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Common Built-in Exceptions

• ZeroDivisionError
• ValueError
• TypeError
• IndexError
• KeyError
• FileNotFoundError

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Exception Handling in Automation Testing

try:
    driver.find_element(By.ID, "login").click()
except Exception as e:
    print("Element not found:", e)

Exception handling is heavily used in:

• Selenium automation
• Robot Framework libraries
• API automation scripts

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Best Practices for Exception Handling

• Catch specific exceptions
• Avoid using bare except
• Use finally to close resources
• Log exceptions instead of ignoring them

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Common Interview Questions

• What is exception handling?
• Difference between error and exception
• What is try-except block?
• What is finally?
• What is a custom exception?

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Conclusion

Exception handling in Python helps you write safe and reliable code. It is a must-have skill for Python developers and automation testers.

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