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>>> import re
>>> match = re.match('Hello[ \t]*(.*)world', 'Hello    Python world')
>>> match.group(1)
'Python '

This example searches for a substring that begins with the word “Hello,” followed by zero or more tabs or spaces, followed by arbitrary characters to be saved as a matched group,

From

Cover of Learning Python, 5th Edition

Note

(.) part is the ones where matches are found. match.groups() will list ones matched where (.) is located.