Python - finding date in a string

Question

I want to be able to read a string and return the first date appears in it. Is there a ready module that I can use? I tried to write regexs for all possible date format, but it is quite long. Is there a better way to do it?

Answer 1

You can run a date parser on all subtexts of your text and pick the first date. Of course, such solution would either catch things that are not dates or would not catch things that are, or most likely both.

Let me provide an example that uses dateutil.parser to catch anything that looks like a date:

import dateutil.parser
from itertools import chain
import re

# Add more strings that confuse the parser in the list
UNINTERESTING = set(chain(dateutil.parser.parserinfo.JUMP, 
                          dateutil.parser.parserinfo.PERTAIN,
                          ['a']))

def _get_date(tokens):
    for end in xrange(len(tokens), 0, -1):
        region = tokens[:end]
        if all(token.isspace() or token in UNINTERESTING
               for token in region):
            continue
        text = ''.join(region)
        try:
            date = dateutil.parser.parse(text)
            return end, date
        except ValueError:
            pass

def find_dates(text, max_tokens=50, allow_overlapping=False):
    tokens = filter(None, re.split(r'(\S+|\W+)', text))
    skip_dates_ending_before = 0
    for start in xrange(len(tokens)):
        region = tokens[start:start + max_tokens]
        result = _get_date(region)
        if result is not None:
            end, date = result
            if allow_overlapping or end > skip_dates_ending_before:
                skip_dates_ending_before = end
                yield date


test = """Adelaide was born in Finchley, North London on 12 May 1999. She was a 
child during the Daleks' abduction and invasion of Earth in 2009. 
On 1st July 2058, Bowie Base One became the first Human colony on Mars. It 
was commanded by Captain Adelaide Brooke, and initially seemed to prove that 
it was possible for Humans to live long term on Mars."""

print "With no overlapping:"
for date in find_dates(test, allow_overlapping=False):
    print date


print "With overlapping:"
for date in find_dates(test, allow_overlapping=True):
    print date

The result from the code is, quite unsurprisingly, rubbish whether you allow overlapping or not. If overlapping is allowed, you get a lot of dates that are nowhere to be seen, and if if it is not allowed, you miss the important date in the text.

With no overlapping:
1999-05-12 00:00:00
2009-07-01 20:58:00
With overlapping:
1999-05-12 00:00:00
1999-05-12 00:00:00
1999-05-12 00:00:00
1999-05-12 00:00:00
1999-05-03 00:00:00
1999-05-03 00:00:00
1999-07-03 00:00:00
1999-07-03 00:00:00
2009-07-01 20:58:00
2009-07-01 20:58:00
2058-07-01 00:00:00
2058-07-01 00:00:00
2058-07-01 00:00:00
2058-07-01 00:00:00
2058-07-03 00:00:00
2058-07-03 00:00:00
2058-07-03 00:00:00
2058-07-03 00:00:00

Essentially, if overlapping is allowed:

1. "12 May 1999" is parsed to 1999-05-12 00:00:00
2. "May 1999" is parsed to 1999-05-03 00:00:00 (because today is the 3rd day of the month)

If, however, overlapping is not allowed, "2009. On 1st July 2058" is parsed as 2009-07-01 20:58:00 and no attempt is made to parse the date after the period.