Question

I am trying to learn python itertools (love it so far!), but I am struck with a problem. I have the following two lists:

a=["http://www.xyz.com/jhuh7287", "http://www.hjuk.com/kashjh716", "http://www.psudjg.com/9279jshkoh", "http://www.xyz.com/jhuh7287",  "http://www.xyz.com/9289jhjbg"]
data=["k","some small string here", "so med string here", "some string here","l"]
tempstring="http://www.xyz.com"

Initially, what I wanted was to remove data[i] for all strings which are below a certain length, and subsequently delete the corresponding entries in a. For this, I used something along the lines of:

iselectors = [x is not len(str(x))>1 for x in data]
data=list(itertools.compress(data, iselectors))
a=list(itertools.compress(a, selectors))

..which works well. Now, I need to add another condition to my iselectors, which states that only when “tempstring is in a[i]” and len(str(x))>1..

So, I have tried something like:

iselectors = [tempstring in a and x is not len(str(x))>1 for x in data]

…but I am not sure this is right, since I do not think I am iterating over the entire a when I use “tempstring in a”

Any guidance would be much appreciated.
Thanks.

Answer 1

Easiest way is to work it through:

>>> pprint(zip(data, a))
[('k', 'http://www.xyz.com/jhuh7287'),
 ('some small string here', 'http://www.hjuk.com/kashjh716'),
 ('so med string here', 'http://www.psudjg.com/9279jshkoh'),
 ('some string here', 'http://www.xyz.com/jhuh7287'),
 ('l', 'http://www.xyz.com/9289jhjbg')]

>>> [ (av, dv) for av, dv in zip(a, data) if len(av) > 1 and tempstring in av]
[('http://www.xyz.com/jhuh7287', 'k'), ('http://www.xyz.com/jhuh7287', 'some string here'), ('http://www.xyz.com/9289jhjbg', 'l')]

So with a bit of refactoring:

selectors = (tempstring in dv for av, dv in izip(a, data) if len(av) > 1)

And since @mgilson deleted his answer with a key point – which I hope the OP has taken on board, I’m going to re-post his wording to this answer:

Also, is is used to compare object identities. While this check works
for small integers in Cpython (1 is len(str(1))), it’s not guaranteed
to work with other python implementations (nor is it guaranteed to
work in Cpython in the future). I think you just want len(str(x))>1.