python-errors-and-exceptions-notes.md

Python Errors and Exceptions

Manually raising an exception

To raise your own exception use the raise method:

raise ValueError('That value not so good')

Here's the documentation on the available exception classes

Handling errors

Like other languages, Python has a try construct:

try:
    raise NameError('Bad name')
except NameError:
    print('Got a name error')
    raise

You can also pass the error message:

try:
    raise NameError('Bad name')
except NameError as err:
    print('Got a name error: "{}"'.format(err))

You can also catch other errors with a final, catchall except:

import sys
try:
    raise ValueError('Bad value')
except NameError as err:
    print('Got a name error: "{}"'.format(err))
except:
    print('Got some other error: "{}"'.format(sys.exc_info()[0]))

You can execute code if not exceptions are raised with and else:

try:
    pass
except NameError as err:
    print('Got a name error: "{}"'.format(err))
else:
    print('No exception raised')

You can execute followup code whether or not an exception is raised with finally:

try:
    pass
except NameError as err:
    print('Got a name error: "{}"'.format(err))
finally:
    print('Always executing this code')