Good use for itertools.dropwhile and itertools.takewhile

Nick Mellor thebalancepro at gmail.com
Tue Dec 4 16:24:07 CET 2012


I love the way you guys can write a line of code that does the same as 20 of mine :)

I can turn up the heat on your regex by feeding it a null description or multiple white space (both in the original file.) I'm sure you'd adjust, but at the cost of a more complex regex.

Meanwhile takewith and dropwith are behaving themselves impeccably but my while loop has fallen over.

Best,

Nick

On Wednesday, 5 December 2012 01:31:48 UTC+11, Vlastimil Brom  wrote:
> 2012/12/4 Nick Mellor <thebalancepro at gmail.com>:
> 
> > Hi,
> 
> >
> 
> > I came across itertools.dropwhile only today, then shortly afterwards found Raymond Hettinger wondering, in 2007, whether to drop [sic] dropwhile and takewhile from the itertools module.
> 
> >
> 
> > Fate of itertools.dropwhile() and itertools.takewhile() - Python
> 
> > bytes.com
> 
> > http://bit.ly/Vi2PqP
> 
> >
> 
> > Almost nobody else of the 18 respondents seemed to be using them.
> 
> >
> 
> > And then 2 hours later, a use case came along. I think. Anyone have any better solutions?
> 
> >
> 
> > I have a file full of things like this:
> 
> >
> 
> > "CAPSICUM RED fresh from Queensland"
> 
> >
> 
> > Product names (all caps, at start of string) and descriptions (mixed case, to end of string) all muddled up in the same field. And I need to split them into two fields. Note that if the text had said:
> 
> >
> 
> > "CAPSICUM RED fresh from QLD"
> 
> >
> 
> > I would want QLD in the description, not shunted forwards and put in the product name. So (uncontrived) list comprehensions and regex's are out.
> 
> >
> 
> > I want to split the above into:
> 
> >
> 
> > ("CAPSICUM RED", "fresh from QLD")
> 
> >
> 
> > Enter dropwhile and takewhile. 6 lines later:
> 
> >
> 
> > from itertools import takewhile, dropwhile
> 
> > def split_product_itertools(s):
> 
> >     words = s.split()
> 
> >     allcaps = lambda word: word == word.upper()
> 
> >     product, description = takewhile(allcaps, words), dropwhile(allcaps, words)
> 
> >     return " ".join(product), " ".join(description)
> 
> >
> 
> >
> 
> > When I tried to refactor this code to use while or for loops, I couldn't find any way that felt shorter or more pythonic:
> 
> >
> 
> > (9 lines: using for)
> 
> >
> 
> > def split_product_1(s):
> 
> >     words = s.split()
> 
> >     product = []
> 
> >     for word in words:
> 
> >         if word == word.upper():
> 
> >             product.append(word)
> 
> >         else:
> 
> >             break
> 
> >     return " ".join(product), " ".join(words[len(product):])
> 
> >
> 
> >
> 
> > (12 lines: using while)
> 
> >
> 
> > def split_product_2(s):
> 
> >     words = s.split()
> 
> >     i = 0
> 
> >     product = []
> 
> >     while 1:
> 
> >         word = words[i]
> 
> >         if word == word.upper():
> 
> >             product.append(word)
> 
> >             i += 1
> 
> >         else:
> 
> >             break
> 
> >     return " ".join(product), " ".join(words[i:])
> 
> >
> 
> >
> 
> > Any thoughts?
> 
> >
> 
> > Nick
> 
> > --
> 
> > http://mail.python.org/mailman/listinfo/python-list
> 
> 
> 
> Hi,
> 
> the regex approach doesn't actually seem to be very complex, given the
> 
> mentioned specification, e.g.
> 
> 
> 
> >>> import re
> 
> >>> re.findall(r"(?m)^([A-Z\s]+) (.+)$", "CAPSICUM RED fresh from QLD\nCAPSICUM RED fresh from Queensland")
> 
> [('CAPSICUM RED', 'fresh from QLD'), ('CAPSICUM RED', 'fresh from Queensland')]
> 
> >>>
> 
> 
> 
> (It might be necessary to account for some punctuation, whitespace etc. too.)
> 
> 
> 
> hth,
> 
>   vbr




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