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pythonregexsubstringcharacter-class

Python regexp to match full or partial word

Is there a way to get regexp to match as much of a specific word as is possible? For example, if I am looking for the following words: yesterday, today, tomorrow

I want the following full words to be extracted:

  • yest
  • yesterday
  • tod
  • toda
  • today
  • tom
  • tomor
  • tomorrow

    The following whole words should fail to match (basically, spelling mistakes):

  • yesteray
  • tomorow
  • tommorrow
  • tody

    The best I could come up with so far is:

    \b((tod(a(y)?)?)|(tom(o(r(r(o(w)?)?)?)?)?)|(yest(e(r(d(a(y)?)?)?)?)?))\b (Example)

    Note: I could implement this using a finite state machine but thought it would be a giggle to get regexp to do this. Unfortunately, anything I come up with is ridiculously complex and I'm hoping that I've just missed something.

    • Solution

  • The regex you are looking for should include optional groups with alternations.

    \b(yest(?:e(?:r(?:d(?:ay?)?)?)?)?|tod(?:ay?)?|tom(?:o(?:r(?:r(?:ow?)?)?)?)?)\b

    See demo

    Note that \b word boundaries are very important since you want to match whole words only.

    Regex explanation:

    • \b - leading word boundary
    • (yest(?:e(?:r(?:d(?:ay?)?)?)?)?|tod(?:ay?)?|tom(?:o(?:r(?:r(?:o(?:w)?)?)?)?)?) - a capturing group matching
      • yest(?:e(?:r(?:d(?:ay?)?)?)?)? - yest, yeste, yester, yesterd, yesterda or yesterday
      • tod(?:ay?)? - tod or toda or today
      • tom(?:o(?:r(?:r(?:o(?:w)?)?)?)?)? - tom, tomo, tomor, tomorr, tomorro, or tomorrow
    • \b - trailing word boundary

    See Python demo:

    import re
p = re.compile(ur'\b(yest(?:e(?:r(?:d(?:ay?)?)?)?)?|tod(?:ay?)?|tom(?:o(?:r(?:r(?:ow?)?)?)?)?)\b', re.IGNORECASE)
test_str = u"yest\nyeste\nyester\nyesterd\nyesterda\nyesterday\ntod\ntoda\ntoday\ntom\ntomo\ntomor\ntomorr\ntomorro\ntomorrow\n\nyesteray\ntomorow\ntommorrow\ntody\nyesteday"
print(p.findall(test_str))
# => [u'yest', u'yeste', u'yester', u'yesterd', u'yesterda', u'yesterday', u'tod', u'toda', u'today', u'tom', u'tomo', u'tomor', u'tomorr', u'tomorro', u'tomorrow']