In the Regular Expression HOWTO
https://docs.python.org/3.6/howto/regex.html#regex-howto
the last example in the "Grouping" section has a bug. The code is supposed to find repeated words, but it catches false repetitions.

>>> p = re.compile(r'(\b\w+)\s+\1')
>>> p.search('Paris in the the spring').group()
'the the'
>>> p.search('k is the thermal coefficient').group()
'the the'

I propose adding a \b after \1, this solves the problem :

>>> p = re.compile(r'(\b\w+)\s+\1\b')
>>> p.search('Paris in the the spring').group()
'the the'
>>> print p.search('k is the thermal coefficient')
None