Regex search to extract float from string. Python

Question

import re

sequence = 'i have -0.03 dollars in my hand'

m = re.search('(have )(-\w[.]+)( dollars\w+)',sequence)

print m.group(0)
print m.group(1)
print m.group(2)

Looking for a way to extract text between two occurrences. In this case, the format is 'i have ' followed by - floats and then followed by ' dollars\w+'

How do i use re.search to extract this float ? Why don't the groups work this way ? I know there's something I can tweak to get it to work with these groups. any help would be greatly appreciated

I thought I could use groups with paranthesis but i got an eror

How can you have -0.03 dollars in your hand? :) – Tim Pietzcker Jan 16 '14 at 08:02 — Tim Pietzcker, Jan 16 '14 at 08:02

score 2 · Accepted Answer · answered Jan 16 '14 at 08:03

-\w[.]+ does not match -0.03 because [.] matches . literally because . is inside the [...].

\w after dollars also prevent the pattern to match the sequence. There no word character after dollars.

Use (-?\d+\.\d+) as pattern:

import re

sequence = 'i have -0.03 dollars in my hand'

m = re.search(r'(have )(-?\d+\.\d+)( dollars)', sequence)

print m.group(1) # captured group start from `1`.
print m.group(2) 
print m.group(3)

BTW, captured group numbers start from 1. (group(0) returns entire matched string)

@draconisthe0ry, `-?` make `-` optional because `?` match 0 or 1 occurrence of `RE`. — falsetru, Jan 16 '14 at 14:22

score 2 · Answer 2 · answered Jan 16 '14 at 08:07

Your regex doesn't match for several reasons:

it always requires a - (OK in this case, questionable in general)
it requires exactly one digit before the . (and it even allows non-digits like A).
it allows any number of dots, but no more digits after the dots.
it requires one or more alphanumerics immediately after dollars.

So it would match "I have -X.... dollarsFOO in my hand" but not "I have 0.10 dollars in my hand".

Also, there is no use in putting fixed texts into capturing parentheses.

m = re.search(r'\bhave (-?\d+\.\d+) dollars\b', sequence)

would make much more sense.

score 0 · Answer 3 · edited May 23 '17 at 12:29

This question has already been asked in many formulations before. You're looking for a regular expression that will find a number. Since number formats may include decimals, commas, exponents, plus/minus signs, and leading zeros, you'll need a robust regular expression. Fortunately, this regular expression has already been written for you.

See How to extract a floating number from a string and Regular expression to match numbers with or without commas and decimals in text

Regex search to extract float from string. Python

3 Answers3

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