[Python-Dev] Another case for frozendict

[R. David Murray]

On Wed, 16 Jul 2014 03:27:23 +0100, MRAB <python at mrabarnett.plus.com> wrote:
> Here's another use-case.
> 
> Using the 're' module:
> 
>  >>> import re
>  >>> # Make a regex.
> ... p = re.compile(r'(?P<first>\w+)\s+(?P<second>\w+)')
>  >>>
>  >>> # What are the named groups?
> ... p.groupindex
> {'first': 1, 'second': 2}
>  >>>
>  >>> # Perform a match.
> ... m = p.match('FIRST SECOND')
>  >>> m.groupdict()
> {'first': 'FIRST', 'second': 'SECOND'}
>  >>>
>  >>> # Try modifying the pattern object.
> ... p.groupindex['JUNK'] = 'foobar'
>  >>>
>  >>> # What are the named groups now?
> ... p.groupindex
> {'first': 1, 'second': 2, 'JUNK': 'foobar'}
>  >>>
>  >>> # And the match object?
> ... m.groupdict()
> Traceback (most recent call last):
>    File "<stdin>", line 2, in <module>
> IndexError: no such group
> 
> It can't find a named group called 'JUNK'.

IMO, preventing someone from shooting themselves in the foot by modifying
something they shouldn't modify according to the API is not a Python
use case ("consenting adults").

> And with a bit more tinkering it's possible to crash Python. (I'll
> leave that as an exercise for the reader! :-))

Preventing a Python program from being able to crash the interpreter,
that's a use case :)

--David