Remove characters except digits from string using Python

Question

How can I remove all characters except numbers from string

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Not a one liner but very simple   buffer      some str    aas30dsa20   for char in some str      if not char isdigit            buffer    char  print  buffer

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x translate None  string digits    will delete all digits from string  To delete letters and keep the digits  do this   x translate None  string letters

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Ugly but works    gt  gt  gt  s  aaa12333bb445bb54b5b52   gt  gt  gt  a      join filter lambda x   x isdigit    s    gt  gt  gt  a  1233344554552   gt  gt  gt

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A fast version for Python 3     xx3 py from collections import defaultdict import string  NoneType   type None   def keeper keep       table   defaultdict  NoneType      table update  ord c   c for c in keep       return table  digit keeper   keeper string digits    Here s a performance comparison vs  regex     python3 3 -mtimeit -s import xx3  x  aaa12333bb445bb54b5b52    x translate xx3 digit keeper   1000000 loops  best of 3  1 02 usec per loop   python3 3 -mtimeit -s import re  r   re compile r  D    x  aaa12333bb445bb54b5b52    r sub     x   100000 loops  best of 3  3 43 usec per loop   So it s a little bit more than 3 times faster than regex  for me   It s also faster than class Del above  because defaultdict does all its lookups in C  rather than  slow  Python   Here s that version on my same system  for comparison     python3 3 -mtimeit -s import xx  x  aaa12333bb445bb54b5b52    x translate xx DD   100000 loops  best of 3  13 6 usec per loop

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import re  string    1abcd2XYZ3  string without letters   re sub r  a-z        string lower     result    123

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my string  quot sdfsdfsdfsfsdf353dsg345435sdfs525436654 dgg  quot   my string    join  ch if ch in  0123456789  else     for ch in my string  print output  my string    output  353345435525436654

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You can easily do it using Regex   gt  gt  gt  import re  gt  gt  gt  re sub   D        70 000   70000

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You can read each character  If it is digit  then include it in the answer  The str isdigit   method is a way to know if a character is digit   your input    12kjkh2nnk34l34  your output      join c for c in your input if c isdigit    print your output     1223434

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along the lines of bayer s answer      join i for i in s if i isdigit

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s    join i for i in s if i isdigit      Another generator variant

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In Python 2    by far the fastest approach is the  translate method    gt  gt  gt  x  aaa12333bb445bb54b5b52   gt  gt  gt  import string  gt  gt  gt  all string maketrans         gt  gt  gt  nodigs all translate all  string digits   gt  gt  gt  x translate all  nodigs   1233344554552   gt  gt  gt     string maketrans makes a translation table  a string of length 256  which in this case is the same as    join chr x  for x in range 256    just faster to make -    translate applies the translation table  which here is irrelevant since all essentially means identity  AND deletes characters present in the second argument -- the key part    translate works very differently on Unicode strings  and strings in Python 3 -- I do wish questions specified which major-release of Python is of interest   -- not quite this simple  not quite this fast  though still quite usable   Back to 2    the performance difference is impressive        python -mtimeit -s import string  all string maketrans          nodig all translate all  string digits   x  aaa12333bb445bb54b5b52    x translate all  nodig   1000000 loops  best of 3  1 04 usec per loop   python -mtimeit -s import re   x  aaa12333bb445bb54b5b52    re sub r  D       x   100000 loops  best of 3  7 9 usec per loop   Speeding things up by 7-8 times is hardly peanuts  so the translate method is well worth knowing and using  The other popular non-RE approach        python -mtimeit -s x  aaa12333bb445bb54b5b52       join i for i in x if i isdigit     100000 loops  best of 3  11 5 usec per loop   is 50  slower than RE  so the  translate approach beats it by over an order of magnitude   In Python 3  or for Unicode  you need to pass  translate a mapping  with ordinals  not characters directly  as keys  that returns None for what you want to delete  Here s a convenient way to express this for deletion of  everything but  a few characters   import string  class Del    def   init   self  keep string digits       self comp   dict  ord c  c  for c in keep    def   getitem   self  k       return self comp get k   DD   Del    x  aaa12333bb445bb54b5b52  x translate DD    also emits  1233344554552    However  putting this in xx py we have        python3 1 -mtimeit -s import re   x  aaa12333bb445bb54b5b52    re sub r  D       x   100000 loops  best of 3  8 43 usec per loop   python3 1 -mtimeit -s import xx  x  aaa12333bb445bb54b5b52    x translate xx DD   10000 loops  best of 3  24 3 usec per loop      which shows the performance advantage disappears  for this kind of  deletion  tasks  and becomes a performance decrease

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I used this   letters  should contain all the letters that you want to get rid of   Output   Input translate  ord i   None for i in  letters      Example   Input    I would like 20 dollars for that suit  Output   Input translate  ord i   None for i in  abcdefghijklmnopqrstuvwxzy     print Output   Output  20

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Use re sub  like so    gt  gt  gt  import re  gt  gt  gt  re sub   D        aas30dsa20    3020     D matches any non-digit character so  the code above  is essentially replacing every non-digit character for the empty string   Or you can use filter  like so  in Python 2     gt  gt  gt  filter str isdigit   aas30dsa20    3020    Since in Python 3  filter returns an iterator instead of a list  you can use the following instead    gt  gt  gt     join filter str isdigit   aas30dsa20     3020

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python -mtimeit -s import re   x  aaa12333bb445bb54b5b52    re sub r  D       x        100000 loops  best of 3  2 48 usec per loop     python -mtimeit -s import re  x  aaa12333bab445bb54b5b52       join re findall   a-z    x         100000 loops  best of 3  2 02 usec per loop     python -mtimeit -s import re   x  aaa12333bb445bb54b5b52    re sub r  D       x        100000 loops  best of 3  2 37 usec per loop     python -mtimeit -s import re  x  aaa12333bab445bb54b5b52       join re findall   a-z    x         100000 loops  best of 3  1 97 usec per loop   I had observed that join is faster than sub

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Use a generator expression    gt  gt  gt  s    foo200bar   gt  gt  gt  new s      join i for i in s if i in  0123456789

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You can use filter   filter lambda x  x isdigit     dasdasd2313dsa     On python3 0 you have to join this  kinda ugly          join filter lambda x  x isdigit     dasdasd2313dsa

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The op mentions in the comments that he wants to keep the decimal place  This can be done with the re sub method  as per the second and IMHO best answer  by explicitly listing the characters to keep e g    gt  gt  gt  re sub    0123456789         poo123 4and5fish    123 45

[python] Remove characters except digits from string using Python?

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