Remove Empty Strings from a List of Strings
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...
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?
13 Answers
I would use filter:
str_list = filter(None, str_list)
str_list = filter(bool, str_list)
str_list = filter(len, str_list)
str_list = filter(lambda item: item, str_list)
Python 3 returns an iterator from filter, so should be wrapped in a call to list()
str_list = list(filter(None, str_list))
Using a list comprehension is the most Pythonic way:
>>> strings = ["first", "", "second"]
>>> [x for x in strings if x]
['first', 'second']
If the list must be modified in-place, because there are other references which must see the updated data, then use a slice assignment:
strings[:] = [x for x in strings if x]
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, ...)
>>> lstr = ['hello', '', ' ', 'world', ' ']
>>> lstr
['hello', '', ' ', 'world', ' ']
>>> ' '.join(lstr).split()
['hello', 'world']
>>> filter(None, lstr)
['hello', ' ', 'world', ' ']
Compare time
>>> from timeit import timeit
>>> timeit('" ".join(lstr).split()', "lstr=['hello', '', ' ', 'world', ' ']", number=10000000)
4.226747989654541
>>> timeit('filter(None, lstr)', "lstr=['hello', '', ' ', 'world', ' ']", number=10000000)
3.0278358459472656
Notice that filter(None, lstr) does not remove empty strings with a space ' ', it only prunes away '' while ' '.join(lstr).split() removes both.
To use filter() with white space strings removed, it takes a lot more time:
>>> timeit('filter(None, [l.replace(" ", "") for l in lstr])', "lstr=['hello', '', ' ', 'world', ' ']", number=10000000)
18.101892948150635
Reply from @Ib33X is awesome. If you want to remove every empty string, after stripped. you need to use the strip method too. Otherwise, it will return the empty string too if it has white spaces. Like, " " will be valid too for that answer. So, can be achieved by.
strings = ["first", "", "second ", " "]
[x.strip() for x in strings if x.strip()]
The answer for this will be ["first", "second"].
If you want to use filter method instead, you can do like
list(filter(lambda item: item.strip(), strings)). This is give the same result.
Sum up best answers:
Must Read
1. Eliminate emtpties WITHOUT stripping:
That is, all-space strings are retained:
slist = list(filter(None, slist))
PROs:
- simplest;
- fastest (see benchmarks below).
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