conditional regex - noticing errors

Question

I have a string that includes an arbitrary number of pairs:

A=B, C=D, E=F

This is an options string, so I know "A", "C", and "E". I can query for them if I want.

I want to find malformed pairs in the string:

A=B, C, E=F  # C has no equals or value
A=, C=D, E=F # A has no value
A=B, C=D, E=F X # what is X doing there!

Of course, A, C, and E are all optional and can appear in any order.

What is the elegant way to grab all the pairs, while noticing an error condition? I am able to grab pairs now using re.findall(...), but I fail in the 3rd case above.

Here's what I have. In my exact case, the right side of the pair must be quoted but that's not important for this question.

re.findall('\s*(\w+)\s*=\s*(?P<Q>[\'\"])(\w*)(P=Q)\s*,{0,1}', a_string)

If I knew that a_string was entirely consumed, I'd be a happy guy.

Avinash Raj · Accepted Answer · 2015-09-14 19:03:34Z

5

Split and print the strings which is not in the pattern like A=B.

>>> def malformed(s):
    return [i for i in s.split(', ') if not re.search(r'^[A-Z]+=[A-Z]+$', i)]

>>> print(malformed('A=, C=D, E=F'))
['A=']
>>> print(malformed('A=B, C=D, E=F X'))
['E=F X']
>>> print(malformed('A=B, C, E=F'))
['C']

answered Sep 14, 2015 at 19:03

Avinash Raj

175k32 gold badges247 silver badges289 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Tony Ennis Over a year ago

Interesting, hitting it from the other direction.

Tony Ennis Over a year ago

By finding the wrong expressions first, you allow a straight-forward regexp find the valid pairs. It is good.

TessellatingHeckler · Accepted Answer · 2015-09-14 19:17:05Z

2

How about splitting it into two much easier to read tests?

import re

tests = ['A=B, C, E=F'
        ,'A=, C=D, E=F'
        ,'A=B, C=D, E=F X'
        ,'A=B, C=D']


for test in tests:

    print "*", test


    if not re.match("^(\w+=\w+, )*(\w+=\w+)$", test):
        print "Options are malformed"

    options = re.findall("\w+=\w+", test)


    print "Read: ", options
    print

Example output:

* A=B, C, E=F
Options are malformed
Read:  ['A=B', 'E=F']

* A=, C=D, E=F
Options are malformed
Read:  ['C=D', 'E=F']

* A=B, C=D, E=F X
Options are malformed
Read:  ['A=B', 'C=D', 'E=F']

* A=B, C=D
Read:  ['A=B', 'C=D']

answered Sep 14, 2015 at 19:17

TessellatingHeckler

29.3k4 gold badges55 silver badges96 bronze badges

Comments

m.cekiera · Accepted Answer · 2015-09-14 19:16:45Z

1

Another approuch would be to try to directly match pairs that don't fit with regex, like:

(?<=,\s|^)(?!\s*\w+=\w+(?=,|$))([^,\n]+)

DEMO

answered Sep 14, 2015 at 19:16

m.cekiera

5,3935 gold badges24 silver badges35 bronze badges

Collectives™ on Stack Overflow

conditional regex - noticing errors

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related