Question

In a program I’m making in python and I want all words formatted like __word__ to stand out. How could I search for words like these using a regex?

Answer 1

Perhaps something like

\b__(\S+)__\b

>>> import re
>>> re.findall(r"\b__(\S+)__\b","Here __is__ a __test__ sentence")
['is', 'test']    
>>> re.findall(r"\b__(\S+)__\b","__Here__ is a test __sentence__")
['Here', 'sentence']
>>> re.findall(r"\b__(\S+)__\b","__Here's__ a test __sentence__")
["Here's", 'sentence']

or you can put tags around the word like this

>>> print re.sub(r"\b(__)(\S+)(__)\b",r"<b>\2<\\b>","__Here__ is a test __sentence__")
<b>Here<\b> is a test <b>sentence<\b>

If you need more fine grained control over the legal word characters it’s best to be explicit

\b__([a-zA-Z0-9_':])__\b  ### count "'" and ":" as part of words

>>> re.findall(r"\b__([a-zA-Z0-9_']+)__\b","__Here's__ a test __sentence:__")
["Here's"]
>>> re.findall(r"\b__([a-zA-Z0-9_':]+)__\b","__Here's__ a test __sentence:__")
["Here's", 'sentence:']