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Re: filter a list of strings

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  Re: filter a list of strings Terry Reedy <tjreedy@udel.edu> - 2015-12-03 11:19 -0500

#99968 — Re: filter a list of strings

On 12/3/2015 7:28 AM, Mark Lawrence wrote:
> On 03/12/2015 01:15, c.buhtz@posteo.jp wrote:
>> I would like to know how this could be done more elegant/pythonic.
>>
>> I have a big list (over 10.000 items) with strings (each 100 to 300
>> chars long) and want to filter them.
>>
>> list = .....
>>
>> for item in list[:]:
>>    if 'Banana' in item:
>>       list.remove(item)
>>    if 'Car' in item:
>>       list.remove(item)
>>
>> There are a lot of more conditions of course. This is just example code.
>> It doesn't look nice to me. To much redundance.
>
> targets = ['Banana', 'Car'...]
> for item in list[:]:
>      for target in targets:
>          if target in item:
>              list.remove(item)
>
>>
>> btw: Is it correct to iterate over a copy (list[:]) of that string list
>> and not the original one?
>>
>
> Absolutely :)

Even better, instead of copying and deleting, which is O(k*n), where n 
is the len of list and k is number deletions, is to create a new list 
with the item you want.  In other words, actually filter, as you said 
you want.

targets = {'Banana', 'Car', ...}  # set intentional
newlist = [item for item in oldlist if item not in targets]

Generically, replace 'not in targets' with any boolean expression or 
function.


-- 
Terry Jan Reedy

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