Question

How do I match words that begin with @ and ends with ;, ., :, or   ?

The words can have any alphanumeric characters and may consist of underscores.

I have come up with ^@([a-zA-Z0-9_])*[:;, ]$ which seems to work for single word sentences alone.

Answer 1

^ matches the start of a string (or line, in multi-line mode), while $ matches the end, so you need to get rid of them:

>>> import re
>>> sentence = "foo bar @match don't match @success;"
>>> re.findall('@([a-zA-Z0-9_])*[:;, ]', sentence)
['h', 's']

It is only capturing the last letter because the qualifier (the *) is outside the brackets matching the capture. Move it inside and you get:

>>> re.findall('@([a-zA-Z0-9_]*)[:;, ]', sentence)
['match', 'success']

If you want to capture the @ and trailing character too, just move them inside the brackets as well:

>>> re.findall('(@[a-zA-Z0-9_]*[:;, ])', sentence)
['@match ', '@success;']

And as mentioned in the comments on the question, you may or may not want to restrict it to a certain number of characters:

>>> sentence = "foo bar @match don't match @somereallylongnamehere @success;"
>>> re.findall('(@[a-zA-Z0-9_]{1,15}[:;, ])', sentence)
['@match ', '@success;']

(Of course, the length restriction could be added to any of the previous expressions, not just this last one).