group 0 in the re module

[MRAB]

On 08/12/2010 02:23, Yingjie Lan wrote:
> Hi,
>
> According to the doc, group(0) is the entire match.
>
>>>> m = re.match(r"(\w+) (\w+)", "Isaac Newton, physicist")
>>>> m.group(0) # The entire match 'Isaac Newton'
>
> But if you do this:
>>>> import re
>>>> re.sub(r'(\d{3})(\d{3})', r'\0 to \1-\2', '757234')
> '\x00 to 757-234'
>
> where I expected
> '757234 to 757-234'
>
> Then I found that in python re '\0' is considered an octal number.
> So, is there anyway to refer to the entire match by an escaped
> notation?
>
Use \g<0>.

This notation works in the replacement template for both named and
numbered groups:

 >>> re.sub(r'(\d{3})(\d{3})', r'\g<0> to \g<1>-\g<2>', '757234')
'757234 to 757-234'
 >>> re.sub(r'(?P<first>\d{3})(?P<second>\d{3})', r'\g<0> to 
\g<first>-\g<second>', '757234')
'757234 to 757-234'