Filtering text in python for numeric values

Question

I know I could use regular expressions to filter text in python for digits, but is that the best way?

Say I have a list of strings:

a="gamma function: 78"
b="factorial value: 120"
c="random number: 33"

is there a good function that would do the following?

for string in [a,b,c]:
    return numbers(string)
78
120
33

best here is meaning 1) easiest, and 2) fastest (computationally), in that order. — rofls, Dec 14 '12 at 21:18
Is there always just one number per string? Is it always an integer? — Tim Pietzcker, Dec 14 '12 at 21:19
ideally yes to both. i will accept an answer that assumes that. — rofls, Dec 14 '12 at 21:20
http://stackoverflow.com/questions/4289331/extract-numbers-of-a-string — tbraun89, Dec 14 '12 at 21:20
semi-related: having an unconditional `return` in a for loop probably won't give you what you want. Ex. `for i in range(3): return i` will return `0`, not `[0,1,2]`. — Kevin, Dec 14 '12 at 21:24

Tim Pietzcker · Accepted Answer · 2022-06-17T15:57:26.180

10

Yes, I'd say regexes are the ideal tool for this:

def numbers(s):
    return int(re.search(r"\d+", s).group(0))

For strings with more than one number:

def numbers(s):
    return [int(match) for match in re.findall(r"\d+", s)]

or even

def numbers(s):
    return (int(match) for match in re.finditer(r"\d+", s))

If you want to join all the digits in your string into a single number:

def numbers(s):
    return int("".join(re.findall(r"\d+", s)))

>>> numbers("abc78def90ghi")
7890

edited Jun 17 '22 at 15:57

answered Dec 14 '12 at 21:22

Tim Pietzcker

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1

A `map` seems in order here: `map(int, re.findall("\d+", s)`. But +1, just what I would do :) – Fred Foo Dec 14 '12 at 21:34
What if the string is like this `78abc98`. Is it possible we can filter out `7898` in the output? – curiouscheese Jun 09 '22 at 03:42

score 0 · Answer 2 · answered Dec 14 '12 at 21:26

0

Just filter out the non-digits in a generator-expression:

a="gamma function: 78"
b="factorial value: 120"
c="random number: 33"

numbers = []
for string in [a,b,c,]:
    numbers.append( int("".join(char for char in string if char.isdigit())))

Pasting this on the console, I got:

>>> numbers
[78, 120, 33]

answered Dec 14 '12 at 21:26

jsbueno

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This is good for one number in each string, even if the digits are sparsed by other chars. Please clarify your question if there are cases in which there may be more than one number in each string - oh, i saw that yes, in your comments now. – jsbueno Dec 14 '12 at 21:28

Filtering text in python for numeric values

2 Answers2