Error handling

Essential to prevent application crashes.

Example without error handling

print(10 / 0)

# ZeroDivisionError: division by zero
# code execution stops here

Use try/except block

Start with try:, end with except. you can use multiple except blocks. you can also use else and finally blocks.

try:
    # code block
    pass
except TypeError as e:
    # this block is executed if TypeError occurs
    pass
except ZeroDivisionError as e:
    # this block is executed if ZeroDivisionError occurs
    pass
except Exception as e:
    # this block is executed if any other error occurs
    # when you do not know the type of error, use this
    pass
else:
    # optional
    # this block is executed if no error occurs
    pass
finally:
    # optional
    # this block is always executed no matter what
    pass

# code execution continues here

Example using try/except block

Here we used multiple errortype in one except block.

try:
    print(10 / 0)
except (ZeroDivisionError, Exception) as e:
    print(e)
    # division by zero

Do not use plain except block

Not recommended. Because you cannot catch the error type.

try:
    print(10 / 0)
except:
    print('Some error occured')

At least use except Exception as e to catch the error.

Use raise to generate an error

def divide(a, b):
    if b == 0:
        # raise an error so that you can catch it later
        raise ValueError('Cannot divide by zero')
    return a / b

try:
    divide(10, 0)
except ValueError as e:
    print(e)
    # Cannot divide by zero

Exception class

All error types are subclasses of the Exception class.