How to Remove All "None" Values From a Python List?

Filtering out all None values from a Python list

You can remove all None values in a Python list in the following ways:

Using filter()

You can simply use the filter() method to filter out all None values from a list, for example, like so:

lst = [1, 2, None, 3, None, 4, 5, None]

filtered_items = filter(lambda item: item is not None, lst)
new_lst = list(filtered_items)

print(new_lst) # [1, 2, 3, 4, 5]
print(filtered_items) # <generator object <genexpr> at ...>

filter(function, iterable) is actually equivalent to the generator expression (item for item in iterable if function(item)).

Using Generator Expression

You can use a generator expression to filter out all None values from a list in the following way:

lst = [1, 2, None, 3, None, 4, 5, None]

filtered_items = (item for item in lst if item is not None)
new_lst = list(filtered_items)

print(new_lst) # [1, 2, 3, 4, 5]
print(filtered_items) # <filter object at ...>

Using generator expression is similar to using list comprehension, however, it is more memory efficient comparatively. This is because list comprehension loads the entire list in memory, whereas a generator expression only loads the current value in memory.

Using List Comprehension

Using list comprehension, you can iterate over a list and return a new list with only items that are not None, for example, like so:

lst = [1, 2, None, 3, None, 4, 5, None]
new_lst = [item for item in lst if item is not None]

print(new_lst) # [1, 2, 3, 4, 5]

Using a Loop

You may iterate over a list using a loop, and selectively add only non-none values, for example, like so:

lst = [1, 2, None, 3, None, 4, 5, None]

new_lst = []
for item in lst:
    if item != None:
        new_lst.append(item)

print(new_lst) #=> [1, 2, 3, 4, 5]

However, it might not be the best choice as it would create/overwrite a variable named "item", which would persist even after the loop completes. Consider, for example, the following where the item variable holds the last value from the original list after the loop completes:

lst = [1, 2, None, 3, None, 4, 5, None]

new_lst = []
for item in lst:
    if item != None:
        new_lst.append(item)

print(item) # None

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