extract digits in a simple way from a python string

Question

I have a string that stores a number and a unit for example   x    120  y     90 Degrees F  banana    200 kgm  orange    300 gm  total weight   banana   orange 1000    and for example I want to add the weights   total weight    200   300 1000   Thanks    I m trying to extract the numbers only to do some operations with these    any idea of what the simplest way to do this  I m only dealing with these two formats i e  digits are at the begining or at the end of the string

User · Accepted Answer

The simplest way to extract a number from a string is to use regular expressions and findall.

>>> import re
>>> s = '300 gm'
>>> re.findall('\d+', s)
['300']
>>> s = '300 gm 200 kgm some more stuff a number: 439843'
>>> re.findall('\d+', s)
['300', '200', '439843']

It might be that you need something more complex, but this is a good first step.

Note that you'll still have to call int on the result to get a proper numeric type (rather than another string):

>>> map(int, re.findall('\d+', s))
[300, 200, 439843]

User · Answer

If you re doing some sort of math with the numbers you might also want to know the units   Given your input restrictions  that the input string contains unit and value only   this should correctly return both  you ll just need to figure out how to convert units into common units for your math    def unit value str       m   re match r     d     d     d      d      str      if m          g   m groups           return     join  g 0   g 2    strip    float g 1       else          return int str

User · Answer

Without using regex  you can just do   def get num x       return int    join ele for ele in x if ele isdigit       Result    gt  gt  gt  get num x  120  gt  gt  gt  get num y  90  gt  gt  gt  get num banana  200  gt  gt  gt  get num orange  300   EDIT    Answering the follow up question   If we know that the only period in a given string is the decimal point  extracting a float is quite easy   def get num x       return float    join ele for ele in x if ele isdigit   or ele            Result    gt  gt  gt  get num  dfgd 45 678fjfjf   45 678

User · Answer

gt  gt  gt  x   120   gt  gt  gt  import string  gt  gt  gt  a string maketrans         gt  gt  gt  ch a translate a  string digits   gt  gt  gt  int x translate a  ch   120

User · Answer

This regular expression handles floats as well  import re re float   re compile r  d     d      You could also add a group to the expression that catches your weight units   re banana   re compile r   P lt number gt  d     d   s   P lt uni gt  a-zA-Z        You can access the named groups like this re banana match  200 kgm   group  number     I think this should help you getting started

[python] extract digits in a simple way from a python string

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