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

[Sven R. Kunze]

On 06.10.2015 13:24, M.-A. Lemburg wrote:
> If you have more than a few values to remove, it's often
> faster to create a new list, since each removal will
> require a copy operation of all trailing items and (every
> now and then) a realloc of the list object to free
> up the unused space:
>
> new_arr = [x
>             for x in arr
>             if x != 1]
>

I think that's a technical detail which can be sorted out in C somehow 
more efficiently.

But the proposal is not about performance rather than readability and 
maintainability.

> On 05.10.2015 22:18, Terry Reedy wrote:
>> The problem with methods is that they only work with one class.  A list.removeall would only remove
>> things equal to a specific item from a list (and presumably in place).  We already have both a
>> generic filter function and syntax that will remove all items from any iterable that meet any
>> condition.  The stream can be fed into any other function that accept an iterable.

remove also removes in-place but it's not overly useful when you know or 
unsure about whether you need to remove an item multiple times.

remove_all would basically complement remove as a more generic alternative.

Btw. one could also think of an additional generalization for this that 
basically takes n arguments which are then removed altogether from the 
list in question:

a = [1,2,3,5,4,2,3,4,1,2]
a.remove_all(1,4,2)
a == [3,5,3]

Just thinking, and I might remember some time where I would have found 
it useful. Not sure.

Best,
Sven