How Can I Efficiently Remove Items from a List During Iteration in Python?

Efficient Item Removal During List Iteration

Iterating over lists while simultaneously removing items can present challenges. One common scenario involves attempting to remove an item based on a specific criterion. Determining the appropriate method for item removal is crucial in such situations.

Solution Strategies

Consider these two efficient approaches:

List Comprehension

Create a new list containing only the desired elements by utilizing list comprehension:

somelist = [x for x in somelist if not determine(x)]

Slice Assignment

Alternatively, modify the existing list directly by assigning to its slice:

somelist[:] = [x for x in somelist if not determine(x)]

This approach is advantageous if multiple references to somelist exist and need to reflect the changes.

Itertools Usage

Itertools provides a convenient approach as well:

Python 2:

from itertools import ifilterfalse
somelist[:] = ifilterfalse(determine, somelist)

Python 3:

from itertools import filterfalse
somelist[:] = filterfalse(determine, somelist)

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