Pythonic/idiomatic?

Ben Finney ben+python at benfinney.id.au
Tue Nov 9 01:26:53 CET 2010


Seebs <usenet-nospam at seebs.net> writes:

> I have a similar situation in a Python context, and I am wondering
> whether this is an idiomatic spelling:
>
> 	' '.join([x for x in target_cflags.split() if re.match('^-[DIiU]', x)])
>
> This appears to do the same thing, but is it an idiomatic use of list
> comprehensions, or should I be breaking it out into more bits?

One thing to know is that, if you want to create a sequence whose only
purpose is to feed to something else and then throw away, a generator
will be cleaner and (probably) better performing than a list.

For this purpose, there is a generator expression syntax
<URL:http://docs.python.org/reference/expressions.html#generator-expressions>,
almost identical to a list comprehension except without the enclosing
brackets.

    ' '.join(x for x in target_cflags.split() if re.match('^-[DIiU]', x))

The regex is less clear for the purpose than I'd prefer. For a simple
“is it a member of this small set”, I'd find it more readable to use a
simple list of the actual strings::

    ' '.join(
        x for x in target_cflags.split()
        if x in ['-D', '-I', '-i', '-U'])

or even an actual set::

    ' '.join(
        x for x in target_cflags.split()
        if x in {'-D', '-I', '-i', '-U'})

The latter works only in Python with set literals (Python 2.7 or later).

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Ben Finney



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