Exceptions

Exceptions are errors detected during runtime. Catching them goes like:

try:
    dangerous_stuff()
    # If that raises an exception, no more of the try clause is
    # executed --- we go straight to looking for a handler.
    print('may not make it here')
except ZeroDivisionError as e:
    # do something with `e` or `e.value`
except NameError:
    # ...
except TypeError:
    # ...
else:
    # Optional. For code that must be executed if no exceptions
    # are raised.
finally:
    print('always executed')

And throw one yourself like so:

raise NameError('Not happy with the name!')

Note Python’s peculiar terminology:

• “catch” in Python is spelled “except”
• “throw” in Python is spelled “raise”

Also:

• An except clause is called “an exception handler”.
• the finally block always runs: whether the exception was caught or not, or even whether or not there was an exception
• See your local Exception doc for the big list of built-in exceptions, including the inheritance hierarchy.
• If you catch an exception but then can’t/won’t deal with it, you can re-raise it with simply raise.
• If you catch the exception, then the code in your relevant except clause runs, the finally block runs (if there is one), and then things merrily go on.
• If you don’t catch the exception, then after the finally block, the exception bubbles up to an outer try block.