Regex: How to match sequence of key-value pairs at end of string

Question

I am trying to match key-value pairs that appear at the end of (long) strings. The strings look like (I replaced the "\n")

my_str = "lots of blah
          key1: val1-words
          key2: val2-words
          key3: val3-words"

so I expect matches "key1: val1-words", "key2: val2-words" and "key3: val3-words".

• The set of possible key names is known.
• Not all possible keys appear in every string.
• At least two keys appear in every string (if that makes it easier to match).
• val-words can be several words.
• key-value pairs should only be matched at the end of string.
• I am using Python re module.

I was thinking

re.compile('(?:tag1|tag2|tag3):')

plus some look-ahead assertion stuff would be a solution. I can't get it right though. How do I do?

Thank you.

/David

Real example string:

my_str = u'ucourt métrage pour kino session volume 18\nThème: O sombres héros\nContraintes: sous titrés\nAuthor: nicoalabdou\nTags: wakatanka productions court métrage kino session humour cantat bertrand noir désir sombres héros mer medine marie trintignant femme droit des femmes nicoalabdou pute soumise\nPosted: 06 June 2009\nRating: 1.3\nVotes: 3'

EDIT:

Based on Mikel's solution I am now using the following:

my_tags = ['\S+'] # gets all tags
my_tags = ['Tags','Author','Posted'] # selected tags
regex = re.compile(r'''
    \n                     # all key-value pairs are on separate lines
    (                      # start group to return
       (?:{0}):            # placeholder for tags to detect '\S+' == all
        \s                 # the space between ':' and value
       .*                  # the value
    )                      # end group to return
    '''.format('|'.join(my_tags)), re.VERBOSE)


regex.sub('',my_str) # return my_str without matching key-vaue lines
regex.findall(my_str) # return matched key-value lines

Answer 1

The negative zero-width lookahead is (?!pattern).

It's mentioned part-way down the re module documentation page.

(?!...)

Matches if ... doesn’t match next. This is a negative lookahead assertion. For example, Isaac (?!Asimov) will match 'Isaac ' only if it’s not followed by 'Asimov'.

So you could use it to match any number of words after a key, but not a key using something like (?!\S+:)\S+.

And the complete code would look like this:

regex = re.compile(r'''
    [\S]+:                # a key (any word followed by a colon)
    (?:
    \s                    # then a space in between
        (?!\S+:)\S+       # then a value (any word not followed by a colon)
    )+                    # match multiple values if present
    ''', re.VERBOSE)

matches = regex.findall(my_str)

Which gives

['key1: val1-words ', 'key2: val2-words ', 'key3: val3-words']

If you print the key/values using:

for match in matches:
    print match

It will print:

key1: val1-words
key2: val2-words
key3: val3-words

Or using your updated example, it would print:

Thème: O sombres héros 
Contraintes: sous titrés 
Author: nicoalabdou 
Tags: wakatanka productions court métrage kino session humour cantat bertrand noir désir sombres héros mer medine marie trintignant femme droit des femmes nicoalabdou pute soumise 
Posted: 06 June 2009 
Rating: 1.3 
Votes: 3

You could turn each key/value pair into a dictionary using something like this:

pairs = dict([match.split(':', 1) for match in matches])

which would make it easier to look up only the keys (and values) you want.

More info:

• Python re module documentation
• Python Regular Expression HOWTO
• Perl Regular Expression Reference "perlreref"

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