7 pat t e r n m at c h I n g w I t h r e g u L a r e X p r e s s I o n s

part of the regex matches zero instances of 
wo
in the string; for 
'Batwoman'
, the 
(wo)*
matches one instance of 
wo
; and for 
'Batwowowowoman'
, 
(wo)*
matches four instances of 
wo
.
If you need to match an actual star character, prefix the star in the 
regular expression with a backslash, 
\*
.

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170
Chapter 7
Matching One or More with the Plus
While 
*
means “match zero or more,” the 
+
(or plus) means “match one or 
more.” Unlike the star, which does not require its group to appear in the 
matched string, the group preceding a plus must appear at least once. It is 
not optional. Enter the following into the interactive shell, and compare it 
with the star regexes in the previous section:
>>> batRegex = re.compile(r'Bat(wo)+man')
>>> mo1 = batRegex.search('The Adventures of Batwoman')
>>> mo1.group()
'Batwoman'
>>> mo2 = batRegex.search('The Adventures of Batwowowowoman')
>>> mo2.group()
'Batwowowowoman'
>>> mo3 = batRegex.search('The Adventures of Batman')
>>> mo3 == None
True
The regex 
Bat(wo)+man
will not match the string 
'The Adventures of 
Batman'
, because at least one 
wo
is required by the plus sign.
If you need to match an actual plus sign character, prefix the plus sign 
with a backslash to escape it: 
\+
.
Matching Specific Repetitions with Braces
If you have a group that you want to repeat a specific number of times, 
follow the group in your regex with a number in braces. For example, the 
regex 
(Ha){3}
will match the string 
'HaHaHa'
, but it will not match 
'HaHa'
, 
since the latter has only two repeats of the 
(Ha)
group.
Instead of one number, you can specify a range by writing a minimum, 
a comma, and a maximum in between the braces. For example, the regex 
(Ha){3,5}
will match 
'HaHaHa'
, 
'HaHaHaHa'
, and 
'HaHaHaHaHa'
.
You can also leave out the first or second number in the braces to leave 
the minimum or maximum unbounded. For example, 
(Ha){3,}
will match 
three or more instances of the 
(Ha)
group, while 
(Ha){,5}
will match zero 
to five instances. Braces can help make your regular expressions shorter. 
These two regular expressions match identical patterns:
(Ha){3}
(Ha)(Ha)(Ha)
And these two regular expressions also match identical patterns:
(Ha){3,5}
((Ha)(Ha)(Ha))|((Ha)(Ha)(Ha)(Ha))|((Ha)(Ha)(Ha)(Ha)(Ha))

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Pattern Matching with Regular Expressions