[Python-ideas] More power in list comprehensions with the 'as' keyword
ziade.tarek at gmail.com
Wed Aug 27 18:51:41 CEST 2008
There's a pattern I am doing all the time: filtering out some elements of a
list, and cleaning them in the same move.
For example, if I have a multi line text, where I want to:
- keep non empty lines
- clean non empty lines
I am doing:
>>> text = """
... this is a multi-line text\t
... muliple lines."""
>>> [l.strip() for l in text.split('\n') if l.strip() != '']
['this is a multi-line text', 'with', 'muliple lines.']
It is not optimal, because I call strip() twice. I could use ifilter then
imap or even use a real loop, but I
want my simple, concise, list comprehension ! And I couldn't find a simple
way to express it.
The pattern can be generically resumed like this :
[transform(e) for e in seq if some_test(transform(e))]
So what about using the 'as' keyword to extend lists comprehensions, and
to avoid calling transform() twice ?
[transform(e) as transformed for e in seq if some_test(transformed)]
In my use case I would simply have to write;:
[l.strip() as stripped for l in text.split('\n') if stripped != '']
Which seems to me clear and concise.
Tarek Ziadé | Association AfPy | www.afpy.org
Blog FR | http://programmation-python.org
Blog EN | http://tarekziade.wordpress.com/
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