[Python-ideas] Proposal how to remove all occurrences of a value from a Python list

[Terry Reedy]

On 10/3/2015 11:05 AM, Eduard Bondarenko wrote:
> Hello everyone,
>
> the main idea of this proposal is to create convenient, maybe more
> Pythonic way to remove all occurrences of a value from a Python list.

This is a special case of in-place filtering.

> Suppose we have list 'arr':
>
>     arr = [1, 2, 3, 1]
>
>
> and we want to remove all 1 from this list.
>
> The most Pythonic way to do it is:
>
>
>     arr[:] = (x for x in arr if x != 1)

arr[:] = filter(lambda x: x != 1, x)

> Looks good, at least for experienced developer, but for Python's
> newcomers solution will look like this:
>
>      >>> while True:
>     ...     try:
>     ...         a.remove(1)
>     ...     except:
>     ...         break
>

Python programmers really must learn either comprehensions or map and 
filter.  They must also learn that repeatedly scanning a sequence should 
be avoided when possible.

> I was surprised that Python doesn't have easy way to remove all occurrences.

The two ways above are pretty easy.

> Currently I am reading "Effective Python" book and I have encounter good
> idea that it's also important to have readable code for new or
> another-language developers. And to my mind current Pythonic 'remove all
> occurrences' is not readable code and does not give insight (at least at
> first glance) into what happens in the code.
>
> This way looks a little bit nicer. I think so..
>
>     a.remove(1, all = True)

I would not mind this, but I don't know if there are enough use cases to 
justify an addition.

-- 
Terry Jan Reedy