CODEWITHSUNDEEP
pythonregex
jollarvia
jollarvia

Reputation: 379

Python matching a real/float number with regex

I'm not the best at re.

Can anyone tell me if this pattern will work to return a single occurrence of a whole or decimal number before the occurrence of the literal,"each"? The number and the string each will be separated by a single space.

for each in parsed:
            if measure_string.find(each)>-1:
                r = re.compile("([0-9]\.?[0-9]?) "+each)
                b = re.match(r,measure_string)
                if b:
                    return b, each

Thanks for taking a look.

Upvotes: 3

Views: 4355

Answers (4)

László Szilágyi
László Szilágyi

Reputation: 729

There is a more precise regexp of the real numbers:

"^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$"

And some check for this regexp:

import re
realnum=re.compile("^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$")

["yes" if realnum.match(test) else "no" for test in ["12", "+12", "-12", "-3.14", ".314e1", "+.01e-12", "+22.134E+2"]]
['yes', 'yes', 'yes', 'yes', 'yes', 'yes', 'yes']

["yes" if realnum.match(test) else "no" for test in ["..12", "+-12", "-12.", "-3.14p", ".314e1.9", "+. 01e-12", "+22.134E"]]
['no', 'no', 'no', 'no', 'no', 'no', 'no']

I have added [eE] option according to Joonho's comment.

Upvotes: 3

Steel Talon
Steel Talon

Reputation: 81

try:

\b(([1-9][0-9]*)?[0-9]\.[0-9]+)\b

to match reals and

\b(([1-9][0-9]*)?[0-9])\b

to match simple.

nice place to test regexes: http://www.regexr.com/

Upvotes: 1

Jules Gagnon-Marchand
Jules Gagnon-Marchand

Reputation: 3781

This will do:

import re
def parse(measure_string,each):
    r = re.compile(r"\d+(\.\d*)?(?=\s"+each+")")
    b = re.match(r, measure_string)
    if(b):
        return b.group(0)

we are using a positive look ahead with ?= in order to match the float only if it's followed by whitespace and the string each, but to not include that whitespace and each in the match. We then return the matched string with MatchObject.group(0) as per the ref.

Upvotes: 0

JustinDanielson
JustinDanielson

Reputation: 3185

[0-9]\.?[0-9]?

The first [0-9] will match once occurrence of a digit. The .? will match 0-1 periods [0-9]? will match 0-1 digits.

So, your regex will parse 1, 11, 1.1, but not 1.11 or 11.1

If you want to parse all of the above, I suggest the following.

([0-9]+(?:\.[0-9]+)?)(?:\s)

[0-9]+ - Match 1 or more digits
\. - Match 1 period
[0-9]*? - Match all remaining digits.
()? - Enter this regex 0 or 1 times.

Anything within parenthesis will be captured. If you see a regex enclosed in (?:...) it is a NON-capturing regex. BUT if that (?...) is enclosed in a (...), it will be captured by the (...) regex... it's kind of messy. But the above should work to capture only the number and not the space.

Upvotes: 3

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