regex - how to capture pattern without different pattern before it?

Question

I'm trying to parse out prices but ignore two patterns that are also prices. One of the exclusions is the total price which is at the end which I am using lookahead to ignore. The second exclusion is if there's a variation of the letter Q before a price, for example Q10.00 or Q AWSMSN11.32 but I want to include if there's a three letter alpha that happens to end in Q such as YMQ234.03.

I've added a negative lookbehind but can't seem to get what I want.

This is the pattern I've tried: (?<![Q\d]) ?M?(\d+\.\d{2})(?=.*\d+\.\d{2}END)

test strings

ABC WS YMQ234.03WS TOY234.03USD468.06END
FUR BB LAB Q10.00 199.00USD209.00END
YAS DG TYY Q AWSMSN11.32 2503.08LD VET Q JKLOLE11.32 2503.08USD5028.80END
PPP VP LAP Q10.00 M342.41EE SFD Q10.00 282.24USD644.65END

regex101

Expected output

+---------------------------------------------------------------------------+---------+---------+
| ABC WS YMQ234.03WS TOY234.03USD468.06END                                  | 234.03  | 234.03  |
| FUR BB LAB Q10.00 199.00USD209.00END                                      | 199.00  |         |
| YAS DG TYY Q AWSMSN11.32 2503.08LD VET Q JKLOLE11.32 2503.08USD5028.80END | 2503.08 | 2503.08 |
| PPP VP LAP Q10.00 M342.41EE SFD Q10.00 282.24USD644.65END                 | 342.41  | 282.24  |
+---------------------------------------------------------------------------+---------+---------+

Answer 1

You could use regex module instead of re with the pattern:

Q[A-Z ]*(?<!\b[A-Z]{2}Q)[\d.]+(*SKIP)(*F)|\d+(?:\.\d+)(?!\d*END$)

See the online demo.

---

In Python this could look like:

import regex
arr = ['ABC WS YMQ234.03WS TOY234.03USD468.06END', 'FUR BB LAB Q10.00 199.00USD209.00END', 'YAS DG TYY Q AWSMSN11.32 2503.08LD VET Q JKLOLE11.32 2503.08USD5028.80END', 'PPP VP LAP Q10.00 M342.41EE SFD Q10.00 282.24USD644.65END']
res = [regex.findall(r'Q[A-Z ]*(?<!\b[A-Z]{2}Q)[\d.]+(*SKIP)(*F)|\d+(?:\.\d+)(?!\d*END$)',x) for x in arr]
print(res)

Prints:

[['234.03', '234.03'], ['199.00'], ['2503.08', '2503.08'], ['342.41', '282.24']]

Answer 2

You might also match what you don't want, and capture what you do want.

Match optional whitespace and uppercase chars where there is a Q and match the decimal value that follows.

Make the exception of eliminating this match asserting that it is not preceded by 2 times an uppercase A-Z followed by Q

After the alternation, capture the decimal value in group 1, asserting that it is not followed by END

\b[A-Z ]*Q[A-Z ]*(?<![A-Z][A-Z]Q)\d+\.\d+|(\d+\.\d{2})(?!END)

Explanation

• \b[A-Z ]*Q[A-Z ]* Word boundary, match a Q between optional spaces and uppercase chars
• (?<![A-Z][A-Z]Q) Negative lookbehind, assert not 2 uppercase chars A-Z followed by Q directly to the left
• \d+\.\d+ Match a decimal value
• | Or
• ( Capture group 1
  • \d+\.\d{2} Match 1+ digits followed by a dot and 2 digits
• ) Close group 1
• (?!END) Negative lookahead, assert what is directly to the right is not END

Regex demo | Python demo

For example

import re

regex = r"\b[A-Z ]*Q[A-Z ]*(?<![A-Z][A-Z]Q)\d+\.\d+|(\d+\.\d{2})(?!END)"
strings = [
    "ABC WS YMQ234.03WS TOY234.03USD468.06END",
    "FUR BB LAB Q10.00 199.00USD209.00END",
    "YAS DG TYY Q AWSMSN11.32 2503.08LD VET Q JKLOLE11.32 2503.08USD5028.80END",
    "PPP VP LAP Q10.00 M342.41EE SFD Q10.00 282.24USD644.65END"
]

for str in strings:
    print('{}: {}'.format(str, [x.group(1) for x in re.finditer(regex, str) if x.group(1)]))

Output

ABC WS YMQ234.03WS TOY234.03USD468.06END: ['234.03', '234.03']
FUR BB LAB Q10.00 199.00USD209.00END: ['199.00']
YAS DG TYY Q AWSMSN11.32 2503.08LD VET Q JKLOLE11.32 2503.08USD5028.80END: ['2503.08', '2503.08']
PPP VP LAP Q10.00 M342.41EE SFD Q10.00 282.24USD644.65END: ['342.41', '282.24']