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...

I would suggest you to have a look at re module. Regular expressions are meant for extracting structured data from corpus. — Sushant Gupta, Apr 28 '12 at 16:07
Your own example shows the issue here. banana is in ``kgm`` and orange is in ``gm``, surely that means that the weights are `200000` and `300`, not `200` and `300`, which adds more complexity to the problem. Does that matter to you?. — Gareth Latty, Apr 28 '12 at 16:09
@jamylak Exactly, is that fixed? Or is that something that could change? — Gareth Latty, Apr 28 '12 at 16:19
I presumed that was not part of the question since it was hard-coded in. — jamylak, Apr 28 '12 at 16:21

score 68 · Accepted Answer · answered Apr 28 '12 at 16:09

68

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]

answered Apr 28 '12 at 16:09

senderle

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will this work for float numbers? I'm very new to python world and I have no clue what the d+ stand for.. thanks for you help :) – Ka Ra Apr 28 '12 at 20:43
1

You can read up on the different regex expressions [here](http://docs.python.org/library/re.html) but `'\d+'` means one or more digits (the + means one or more). – jamylak Apr 28 '12 at 23:43
@KaRa 'd' stands for 'any decimal digit', and '+' stands for 'match 1 or more repetitions'. For more details have a look at https://docs.python.org/2/library/re.html. – Danijel Oct 06 '14 at 11:03
@KaRa You should learn about regex expressions. Such as `import re re.findall("[a-z]", "abcccd ff")` gets all lowercase letters (a-z) one by one in the string `"abcccd ff"` – rassa45 Sep 15 '15 at 19:20
Another approach !!! but only if you have one number in your string !!! will be int(filter(str.isdigit, ' 90 Degrees F')) 90 int(filter(str.isdigit, '$120')) 120 int(filter(str.isdigit, '200 kgm')) 200 int(filter(str.isdigit, '300 gm')) 300 because (filter(str.isdigit, '300 gm 90')) 30090 – dfostic Apr 05 '16 at 18:51

Akavall · Answer 2 · 2012-04-28T23:38:29.990

32

Without using regex, you can just do:

def get_num(x):
    return int(''.join(ele for ele in x if ele.isdigit()))

Result:

>>> get_num(x)
120
>>> get_num(y)
90
>>> get_num(banana)
200
>>> 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:

>>> get_num('dfgd 45.678fjfjf')
45.678

edited Apr 28 '12 at 23:38

answered Apr 28 '12 at 16:37

Akavall

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Awesome! is there anyway to edit this to make also work for float? is it correct to correct to change the return statement to float ? – Ka Ra Apr 28 '12 at 18:56
1

This won't work if there are multiple numbers – rassa45 Sep 15 '15 at 19:20

Francis · Answer 3 · 2012-04-28T16:26:17.087

4

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<number>\d*\.?\d+)\s?(?P<uni>[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.

edited Apr 28 '12 at 16:26

answered Apr 28 '12 at 16:12

Francis

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This does not handle scientific notation or many other interesting floating point values (e.g. nan, inf) – Bklyn Feb 17 '17 at 15:32
banana = '200 kgm' orange = '300 gm' banana = int(banana.replace('kgm', ' ')) orange = int (orange.replace('gm', ' ')) print (banana) print (orange) total_weight = (banana + (orange/1000 )) print (total_weight) – Diwakar SHARMA Oct 05 '19 at 16:18

score 1 · Answer 4 · edited Nov 21 '15 at 11:46

1

>>> x='$120'
>>> import string
>>> a=string.maketrans('','')
>>> ch=a.translate(a, string.digits)
>>> int(x.translate(a, ch))
120

edited Nov 21 '15 at 11:46

demonplus

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answered Apr 28 '12 at 16:10

shiva

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1

This doesn't work... try it for yourself – jamylak Apr 28 '12 at 16:11
@jaymylak thanks for pointing it.rectified – shiva Apr 28 '12 at 16:20

score 0 · Answer 5 · answered Apr 28 '12 at 16:32

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)

extract digits in a simple way from a python string

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