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

Question

want to remove a value from a list if it exists in the list (which it may not).

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

del a[b]
print(a)

The above case (in which it does not exist) 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?

Answer 1

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]

Answer 2

The effects of the three different methods to remove an element from a list:

remove removes the first matching value, not a specific index:

>>> a = [0, 2, 3, 2]
>>> a.remove(2)
>>> a
[0, 3, 2]

del removes the item at a specific index:

>>> a = [9, 8, 7, 6]
>>> del a[1]
>>> a
[9, 7, 6]

and pop removes the item at a specific index and returns it.

>>> a = [4, 3, 5]
>>> a.pop(1)
3
>>> a
[4, 5]

Their error modes are different too:

>>> a = [4, 5, 6]
>>> a.remove(7)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: list.remove(x): x not in list
>>> del a[7]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list assignment index out of range
>>> a.pop(7)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: pop index out of range

Answer 3

There are three ways in which you can Remove elements from List:

1. Using the remove() method.
2. Using the list object's pop() method.
3. Using the del operator.

In Python, list 's methods clear() , pop() , and remove() are used to remove items (elements) from a list. It is also possible to delete items using del statement by specifying a position or range with an index or slice.