What is \1 here?

[Dave Angel]

satishmlmlml at gmail.com Wrote in message:
> What does \1 do in the following piece of code(fourth line)?
> import re
> print(re.sub('[ABC]', '*', 'XAXAXBXBXCXC'))
> print(re.sub('[ABC]_', '*', 'XA-XA_XB-XB_XC-XC_'))
> print(re.sub('(.) spam', 'spam\\1', 'x spam, y spam'))
> def mapper(matchobj):
>        return 'spam' + matchobj.group(1)
> print(re.sub('(.) spam', mapper, 'x spam, y spam'))
> 
> 

Recommend you use raw strings when defining regex patterns.  Then
 you wouldn't have to double the backslash.

To see what re.sub will see, try
print ('spam\\1')

As for what the function does with that, I'll have to guess, as I
 don't do regex. I'd guess it'll match any digit.

-- 
DaveA