Remove empty strings from a list of strings

Question

I want to remove all empty strings from a list of strings in python.

My idea looks like this:

while '' in str_list:
    str_list.remove('')

Is there any more pythonic way to do this?

Answer 1

I guess list comprehensions

list = ["first", "", "second"]
[x for x in list if x]

Output: ['first', 'second']

Edit: Shortened as suggested

Answer 2

Loop through the existing string list and then check for a empty string, if it's not empty populate a new string list with the non-empty values and then replace the old string list with the new string list

Answer 3

I would use filter:

str_list = filter(None, str_list) # fastest
str_list = filter(bool, str_list) # fastest
str_list = filter(len, str_list)  # a bit of slower
str_list = filter(lambda item: item, str_list) # slower than list comprehension

Tests:

>>> timeit('filter(None, str_list)', 'str_list=["a"]*1000', number=100000)
2.4797441959381104
>>> timeit('filter(bool, str_list)', 'str_list=["a"]*1000', number=100000)
2.4788150787353516
>>> timeit('filter(len, str_list)', 'str_list=["a"]*1000', number=100000)
5.2126238346099854
>>> timeit('[x for x in str_list if x]', 'str_list=["a"]*1000', number=100000)
13.354584932327271
>>> timeit('filter(lambda item: item, str_list)', 'str_list=["a"]*1000', number=100000)
17.427681922912598

Answer 4

Depending on the size of your list, it may be most efficient if you use list.remove() rather than create a new list:

l = ["1", "", "3", ""]

while True:
  try:
    l.remove("")
  except ValueError:
    break

This has the advantage of not creating a new list, but the disadvantage of having to search from the beginning each time, although unlike using while '' in l as proposed above, it only requires searching once per occurrence of '' (there is certainly a way to keep the best of both methods, but it is more complicated).

Answer 5

filter actually has a special option for this:

filter(None, sequence)

It will filter out all elements that evaluate to False. No need to use an actual callable here such as bool, len and so on.

It's equally fast as map(bool, ...)