pythonregex

Regex match only if odd number of a character precede and follow

I want to match the closing quote together with the opening quote of the following string if both are on the same line. Two strings may be separated either by a blank or a blank-plus-blank  + .

Regex engine: Python

F.i. from

this is "some string" "; which should match" 234
"and this" + "should also match\"" "\"and this" 
but not this: " " a " + "

I'd like to see matches for:

So in fact, I think it might be best to only match the groups " " and " + " if there is an odd number of quotes before and after the group. Since lookbehing/ahead is fixed length only, I didn't find a good way to do it.

I tried

re.compile(r'(" \+ ")|(" ")(?!;|,)')

but this assumes that there may be no semicolon within a string

and also

re.compile(r'"[^"]+")

but this only finds the strings themselves, but not the "inter-string" quotes.

Solution

  • Here's the character loop parsing method I mentioned above. I track whether we are inside a quote or not, and I track the characters between quotes.

    
data = """\
this is "some string" "; which should match" 234
"and this" + "should also match\\"" "\\"and this" 
but not this: " " a " + "
"""

def check(line):
    in_quotes = False
    between = "xxxx"
    found = []
    escape = False

    for c in line:
        if escape:
            escape = False
        elif c == '"':
            if not in_quotes and between in (' ', ' + '):
                found.append( between )
            between = ""
            in_quotes = not in_quotes
        elif c == '\\':
            escape = True
        elif not in_quotes:
            between += c
    return found

for line in data.splitlines():
    print(line)
    matches = check(line)
    print(matches)

    Output:

    this is "some string" "; which should match" 234
[' ']
"and this" + "should also match\"" "\"and this" 
[' + ', ' ']
but not this: " " a " + "
[]