Is there a simple way to delete a list element by value?


Question

a = [1, 2, 3, 4]
b = a.index(6)

del a[b]
print a

The above shows the following error:

Traceback (most recent call last):
  File "D:\zjm_code\a.py", line 6, in <module>
    b = a.index(6)
ValueError: list.index(x): x not in list

So I have to do this:

a = [1, 2, 3, 4]

try:
    b = a.index(6)
    del a[b]
except:
    pass

print a

But is there not a simpler way to do this?

1
867
4/3/2019 6:58:48 PM

Accepted Answer

To remove an element's first occurrence in a list, simply use list.remove:

>>> a = ['a', 'b', 'c', 'd']
>>> a.remove('b')
>>> print a
['a', 'c', 'd']

Mind that it does not remove all occurrences of your element. Use a list comprehension for that.

>>> a = [10, 20, 30, 40, 20, 30, 40, 20, 70, 20]
>>> a = [x for x in a if x != 20]
>>> print a
[10, 30, 40, 30, 40, 70]
1437
1/29/2018 1:54:49 PM

Usually Python will throw an Exception if you tell it to do something it can't so you'll have to do either:

if c in a:
    a.remove(c)

or:

try:
    a.remove(c)
except ValueError:
    pass

An Exception isn't necessarily a bad thing as long as it's one you're expecting and handle properly.


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