How do I find one number in a string in Python?

Question

I have a file called something like FILE-1.txt or FILE-340.txt. I want to be able to get the number from the file name. I've found that I can use

numbers = re.findall(r'\d+', '%s' %(filename))

to get a list containing the number, and use numbers[0] to get the number itself as a string... But if I know it is just one number, it seems roundabout and unnecessary making a list to get it. Is there another way to do this?

Edit: Thanks! I guess now I have another question. Rather than getting a string, how do I get the integer?

Do I understand it correctly, that by `'%s' %(filename)` you are converting a string to string? If `filename` is a string, then just replace `'%s' %(filename)` with `filename`. — Tadeck, Nov 22 '11 at 22:21
Adding to Tadeck's comment, if `filename` is not a string then `str(filename)` is equivalent to `'%s' % filename`. — Andrew Clark, Nov 22 '11 at 22:23

score 19 · Accepted Answer · answered Nov 22 '11 at 22:19

19

Use search instead of findall:

number = re.search(r'\d+', filename).group()

Alternatively:

number = filter(str.isdigit, filename)

answered Nov 22 '11 at 22:19

Andrew Clark

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Although `filter` is more similar to `re.findall` in cases where there are multiple groups of numbers e.g. using _"FILE-340-1.txt"_ `filter` produces _"3401"_ while `re.search` only returns the first group _"340"_. – Matthew Wilcoxson Jul 18 '13 at 11:45

score 2 · Answer 2 · edited Nov 23 '11 at 14:24

2

Adding to F.J's comment, if you want an int, you can use:

numbers = int(re.search(r'\d+', filename).group())

edited Nov 23 '11 at 14:24

Justin

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answered Nov 23 '11 at 14:01

ewegesin

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score 1 · Answer 3 · answered Nov 22 '11 at 22:25

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If you want your program to be effective

use this:

num = filename.split("-")[1][:-4]

this will work only to the example that you showed

answered Nov 22 '11 at 22:25

Oded BD

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It is take the second part from the splitting and than cut the last 4 chars[".txt"] – Oded BD Nov 22 '11 at 22:47

score 1 · Answer 4 · answered Nov 22 '11 at 22:29

1

Another way just for fun:

In [1]: fn = 'file-340.txt'

In [2]: ''.join(x for x in fn if x.isdigit())
Out[2]: '340'

answered Nov 22 '11 at 22:29

Facundo Casco

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score 0 · Answer 5 · edited Dec 20 '12 at 06:46

0

In response to your new question you can cast the string to an int:

>>>int('123')
123

edited Dec 20 '12 at 06:46

akjoshi

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answered Dec 20 '12 at 06:23

ogama8

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How do I find one number in a string in Python?

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