Question

I’m trying to parse a file in which quotation files are used to encapsulate strings. For instance, the file might contain a line like this:

    "\"Hello there, my friends,\" the tour guide says." me @ swap notify

But it might also contain lines like this:

    "I'm a dingus who wants to put a backslash at the end of my statements. \\" me @ swap notify

In that example, the quotes shouldn’t be escaped, but a single backslash should remain.

Is there any function I can use to extract that full quoted statement? \n for newline and \r for carriage return also show up on occasion, so I’d like to get those two, but only after I have the full string isolated.

Answer 1

1. Parse out the string part. You could use a regular expression or string partition
2. ast.literal_eval the string and assign it to a variable.

Test:

>>> import re
>>> import ast
>>> with open('test.txt.') as f:
...  for line in f:
...   m = re.match('(.*) \w+ @ \w+ \w+', line)
...   print ast.literal_eval(m.group(1))
...
"Hello there, my friends," the tour guide says.
I'm a dingus who wants to put a backslash at the end of my statements. \

The regex says “Match anything and store it as group 1, up to a space, a word, a space, @-sign, space and a word”. You then retreive the group with the .group(1) syntax. The parenthesis define a group, see regex documentation.

Here’s a version that tries to parse the string as greedily as possible, by failing and retrying until a match is found, or no match can be made:

import re
import ast

def match_line(line):
    while line:
        print "Trying to match:", line
        try:
            return ast.literal_eval(line)
        except SyntaxError, e:
            line = line[:e.offset - 1]
        except ValueError: # No way it would ever match
            break
    return None

with open('test.txt.') as f:
    for line in f:
        match = match_line(line.strip())
        print "Matched:", match
        print