[Tutor] A Python idiom that I don't get

[w chun]

> >      prefix = os.path.commonprefix(filter( bool, lines ))

that is an interesting and yes, not very optimal way of saving the set
of non-blank lines.  the commonprefix() function takes a list of
pathnames and returns the longest prefix that all strings have in
common, presumably for disk filenames, although this sounds like just
a string processing function that would work with non-pathnames too.


> > and I don't understand what that 'bool' is doing.  Or rather, I think
> > that I see what it is doing, but I am not sure - and I don't much like it.
>    :
> > I tried replacing 'bool'...

it sounds like you did not develop the original code.  it seems to
work... why are you trying to replace it?  are you refactoring?


> This works but it isn't doing what you think it is.
> lambda True: True
> is the same as
> lambda x: x

kent is right.  True is not a keyword, so you are just using "True" as
a variable name.  scarily, one can do stuff like this:

>>> True, False = False, True
>>> True
False
>>> False
True


> Try filter(None, lines) or use a list comprehension:
> [ line for line in lines if line ]

i like both of these better... they will perform better than with
bool().  of the two, it would be interesting to study which one's
faster... and why.

-wesley