Check for regular expression in a list

[Peter Otten]

Jussi Piitulainen wrote:

> Surely that should be:
> 
>     if not 'firefox' in (i.name() for i in process_iter()):
> 
> And that again should be:
> 
>     if any((i.name() == 'firefox') for i in process_iter()):

The previous one certainly looks better than this, particularly if you move 
the `not` where it belongs:

      if 'firefox' not in (i.name() for i in process_iter()):

Of course you had the next modification in mind when you suggested the above 
modificaton.

> Which can then be made into:
> 
>     if any(i.name().startswith('firefox') for i in process_iter()):
> 
> Or use a regex match if the condition becomes more complex. Even then,
> there is re.match to attemp a match at the start of the string, which
> helps to keep the expression simple.

If regular expression objects were to support equality tests in the rigtht 
way we could stick with the containment test:

>>> def process_names():
...     return (p.name() for p in process_iter())
... 
>>> list(process_names())
['foo', 'bar', 'firefox42', 'baz']
>>> 
>>> class Match:
...     def __init__(self, regex, *args, **kw):
...         self._match = re.compile(regex, *args, **kw).match
...     def __eq__(self, other):
...         try:
...             return self._match(other)
...         except TypeError:
...             return False
... 

With the above hidden under the rug the following is quite readable:

>>> Match("FIRE") in process_names()
False
>>> Match("FIRE", re.IGNORECASE) in process_names()
True
>>> Match("FIRE", re.IGNORECASE) not in process_names()
False
>>> Match("FIRE", re.IGNORECASE) in range(3)
False