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

User · Answer

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, ...)

User · Answer

match using a regular expression and a filter lstr     hello             world        r re compile    A-Za-z0-9     results list filter r match lstr   print results

User · Answer

Keep in mind that if you want to keep the white spaces within a string  you may remove them unintentionally using some approaches  If you have this list    hello world              hello    what you may want   hello world   hello    first trim the list to convert any type of white space to empty string   space to empty    x strip   for x in  text list    then remove empty string from them list  space clean list    x for x in space to empty if x

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Using a list comprehension is the most Pythonic way    gt  gt  gt  strings     first        second    gt  gt  gt   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

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Sum up best answers   1  Eliminate emtpties WITHOUT stripping   That is  all-space strings are retained   slist   list filter None  slist     PROs    simplest  fastest  see benchmarks below     2  To eliminate empties after stripping      2 a     when strings do NOT contain spaces between words   slist       join slist  split     PROs    small code fast   BUT not fastest with big datasets due to memory  contrary to what  paolo-melchiorre results    2 b     when strings contain spaces between words   slist   list filter str strip  slist     PROs    fastest  understandability of the code    Benchmarks on a 2018 machine      Build test-data   import random  string nwords   10000 maxlen   30 null ratio   0 1 rnd   random Random 0                     deterministic results words          rnd randint 0  maxlen           if rnd random    gt   1 - null ratio           else             join random choices string ascii letters  k rnd randint 0  maxlen             for  i in range nwords                Test functions   def nostrip filter slist       return list filter None  slist    def nostrip comprehension slist       return  s for s in slist if s   def strip filter slist       return list filter str strip  slist    def strip filter map slist        return list filter None  map str strip  slist      def strip filter comprehension slist      waste memory     return list filter None   s strip   for s in slist     def strip filter generator slist       return list filter None   s strip   for s in slist     def strip join split slist      words without    spaces     return     join slist  split       Benchmarks    timeit nostrip filter words  142   s    16 8   s per loop  mean    std  dev  of 7 runs  10000 loops each    timeit nostrip comprehension words  263   s    19 1   s per loop  mean    std  dev  of 7 runs  1000 loops each    timeit strip filter words  653   s    37 5   s per loop  mean    std  dev  of 7 runs  1000 loops each    timeit strip filter map words  642   s    36   s per loop  mean    std  dev  of 7 runs  1000 loops each    timeit strip filter comprehension words  693   s    42 2   s per loop  mean    std  dev  of 7 runs  1000 loops each    timeit strip filter generator words  750   s    28 6   s per loop  mean    std  dev  of 7 runs  1000 loops each    timeit strip join split words  796   s    103   s per loop  mean    std  dev  of 7 runs  1000 loops each

User · Answer

As reported by Aziz Alto filter None  lstr  does not remove empty strings with a space     but if you are sure lstr contains only string you can use filter str strip  lstr    gt  gt  gt  lstr     hello             world         gt  gt  gt  lstr   hello             world         gt  gt  gt      join lstr  split     hello    world    gt  gt  gt  filter str strip  lstr    hello    world     Compare time on my pc   gt  gt  gt  from timeit import timeit  gt  gt  gt  timeit      join lstr  split      lstr   hello             world          number 10000000  3 356455087661743  gt  gt  gt  timeit  filter str strip  lstr     lstr   hello             world          number 10000000  5 276503801345825   The fastest solution to remove    and empty strings with a space     remains     join lstr  split     As reported in a comment the situation is different if your strings contain spaces    gt  gt  gt  lstr     hello             world            see you    gt  gt  gt  lstr   hello             world            see you    gt  gt  gt      join lstr  split     hello    world    see    you    gt  gt  gt  filter str strip  lstr    hello    world    see you     You can see that filter str strip  lstr  preserve strings with spaces on it but     join lstr  split   will split this strings

User · Answer

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

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Use filter   newlist filter lambda x  len x  gt 0  oldlist     The drawbacks of using filter as pointed out is that it is slower than alternatives  also  lambda is usually costly     Or you can go for the simplest and the most iterative of all     I am assuming listtext is the original list containing  possibly  empty items for item in listtext      if item          newlist append str item     You can remove str   based on the content of your original list   this is the most intuitive of the methods and does it in decent time

User · Answer

For a list with a combination of spaces and empty values  use simple list comprehension -    gt  gt  gt  s     I    am    a        great                   person          Do    you    think    its    a        a        joke                                        So  you can see  this list has a combination of spaces and null elements  Using the snippet -    gt  gt  gt  d    x for x in s if x strip     gt  gt  gt  d  gt  gt  gt  d     I    am    a    great    person          Do    you    think    its    a    a    joke

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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

User · Answer

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

User · Answer

Instead of if x  I would use if X       in order to just eliminate empty strings  Like this   str list    x for x in str list if x          This will preserve None data type within your list  Also  in case your list has integers and 0 is one among them  it will also be preserved   For example   str list    None      0   Hi        Hello    x for x in str list if x         None  0   Hi    Hello

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gt  gt  gt  lstr     hello             world         gt  gt  gt  lstr   hello             world          gt  gt  gt      join lstr  split     hello    world     gt  gt  gt  filter None  lstr    hello         world          Compare time   gt  gt  gt  from timeit import timeit  gt  gt  gt  timeit      join lstr  split      lstr   hello             world          number 10000000  4 226747989654541  gt  gt  gt  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    gt  gt  gt  timeit  filter None   l replace          for l in lstr      lstr   hello             world          number 10000000  18 101892948150635

[python] Remove empty strings from a list of strings

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