Remove elements as you traverse a list in Python

Question

In Java I can do by using an Iterator and then using the .remove() method of the iterator to remove the last element returned by the iterator, like this:

import java.util.*;

public class ConcurrentMod {
    public static void main(String[] args) {
        List<String> colors = new ArrayList<String>(Arrays.asList("red", "green", "blue", "purple"));
        for (Iterator<String> it = colors.iterator(); it.hasNext(); ) {
            String color = it.next();
            System.out.println(color);
            if (color.equals("green"))
                it.remove();
        }
        System.out.println("At the end, colors = " + colors);
    }
}

/* Outputs:
red
green
blue
purple
At the end, colors = [red, blue, purple]
*/

How would I do this in Python? I can't modify the list while I iterate over it in a for loop because it causes stuff to be skipped (see here). And there doesn't seem to be an equivalent of the Iterator interface of Java.

Answer 1

Best approach in Python is to make a new list, ideally in a listcomp, setting it as the [:] of the old one, e.g.:

colors[:] = [c for c in colors if c != 'green']

NOT colors = as some answers may suggest -- that only rebinds the name and will eventually leave some references to the old "body" dangling; colors[:] = is MUCH better on all counts;-).

Answer 2

iterate over a copy of the list:

for c in colors[:]:
    if c == 'green':
        colors.remove(c)

Answer 3

You could use filter function:

>>> colors=['red', 'green', 'blue', 'purple']
>>> filter(lambda color: color != 'green', colors)
['red', 'blue', 'purple']
>>>

Answer 4

or you also can do like this

>>> colors = ['red', 'green', 'blue', 'purple']
>>> if colors.__contains__('green'):
...     colors.remove('green')