How can I ignore ValueError when I try to remove an element from a list?

Question

How can I ignore the "not in list" error message if I call a.remove(x) when x is not present in list a?

This is my situation:

>>> a = range(10) >>> a [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> a.remove(10) Traceback (most recent call last):   File "<stdin>", line 1, in <module> ValueError: list.remove(x): x not in list >>> a.remove(9) 

Answer 1

A good and thread-safe way to do this is to just try it and ignore the exception:

try:     a.remove(10) except ValueError:     pass  # do nothing! 

Answer 2

I'd personally consider using a set instead of a list as long as the order of your elements isn't necessarily important. Then you can use the discard method:

>>> S = set(range(10)) >>> S set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9]) >>> S.remove(10) Traceback (most recent call last):   File "<stdin>", line 1, in <module> KeyError: 10 >>> S.discard(10) >>> S set([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])