pablouche pablouche - 3 months ago 32
Python Question

Python: Extract numbers from a string

I would extract all the numbers contained in a string. Which is the better suited for the purpose, regular expressions or the

isdigit()
method?

Example:

line = "hello 12 hi 89"


Result:

[12, 89]

Answer

If you only want to extract only positive integers, try the following:

>>> str = "h3110 23 cat 444.4 rabbit 11 2 dog"
>>> [int(s) for s in str.split() if s.isdigit()]
[23, 11, 2]

I would argue that this is better than the regex example for three reasons. First, you don't need another module; secondly, it's more readable because you don't need to parse the regex mini-language; and third, it is faster (and thus likely more pythonic):

python -m timeit -s "str = 'h3110 23 cat 444.4 rabbit 11 2 dog' * 1000" "[s for s in str.split() if s.isdigit()]"
100 loops, best of 3: 2.84 msec per loop

python -m timeit -s "import re" "str = 'h3110 23 cat 444.4 rabbit 11 2 dog' * 1000" "re.findall('\\b\\d+\\b', str)"
100 loops, best of 3: 5.66 msec per loop

This will not recognize floats, negative integers, or integers in hexadecimal format. If you can't accept these limitations, slim's answer below will do the trick.

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