Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #99955 > unrolled thread

Re: filter a list of strings

Back to article view | Back to comp.lang.python

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: filter a list of strings Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-12-03 12:28 +0000
    Re: filter a list of strings Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-12-08 23:58 +0100
      Shadowing built-ins [was Re: filter a list of strings] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-12-09 18:38 +1100
      Re: filter a list of strings Sivan Greenberg <sivan@vitakka.co> - 2015-12-09 16:35 +0200

#99955 — Re: filter a list of strings

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 :)

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence

[toc] | [next] | [standalone]

#100178

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 = .....
>> […]
> 
> 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 :)

However, “list” is a built-in class/constructor that would be overwritten 
this way.  One should choose another identifier than “list” for one’s 
variables.

-- 
PointedEars

Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.

[toc] | [prev] | [next] | [standalone]

#100185 — Shadowing built-ins [was Re: filter a list of strings]

On Wednesday 09 December 2015 09:58, Thomas 'PointedEars' Lahn wrote:

> 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 = .....
>>> […]
[...]
> However, “list” is a built-in class/constructor that would be overwritten
> this way.  One should choose another identifier than “list” for one’s
> variables.

Correct, well mostly correct.

The original built-in list is *not* overridden, as such, but shadowed: it 
still exists, but access to it is blocked by the local variable "list". The 
list *type* still exists, only the *name* list is shadowed. So you can 
easily recover from accidentally shadowing the name by deleting the local:

del list

To beginners, accidental shadowing of built-ins is a serious source of 
confusion. But to experts, intentional shadowing can be useful.

There's nothing wrong with (say):

def sort_and_pop(list):
    list.sort()
    list.pop(0)

Yes, the local "list" shadows the built-in list. So what?

More usefully, one can monkey-patch a module by shadowing a built-in in that 
module:

# Python 3 only.
import builtins
def print(*args, **kwargs):
    log_something()
    builtins.print(*args, **kwargs)




-- 
Steve

[toc] | [prev] | [next] | [standalone]

#100199

That might also work:

new_list = [i for i in the_list if i not in targets]
# given you have no special requirements for the selection
# out of 'targets'

-Sivan

On Wed, Dec 9, 2015 at 12:58 AM, Thomas 'PointedEars' Lahn <
PointedEars@web.de> wrote:

> 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 = .....
> >> […]
> >
> > 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 :)
>
> However, “list” is a built-in class/constructor that would be overwritten
> this way.  One should choose another identifier than “list” for one’s
> variables.
>
> --
> PointedEars
>
> Twitter: @PointedEars2
> Please do not cc me. / Bitte keine Kopien per E-Mail.
> --
> https://mail.python.org/mailman/listinfo/python-list
>



-- 
Sivan Greenberg
Co founder & CTO
Vitakka Consulting

[toc] | [prev] | [standalone]

Back to top | Article view | comp.lang.python

csiph-web