Simple Python sub -


i have following code: 

import re    temp = "c4" num = 5 temp = re.sub(r'(\w)\d',r'\1%s'%num, temp) print temp

i following error:

ps c:\...> .\try.py traceback (most recent call last):   file "c:\...\try.py", line 10, in <module>     temp = re.sub(r'(\w)\d',r'\1%s'%num, temp)   file "c:\python27\lib\re.py", line 151, in sub     return _compile(pattern, flags).sub(repl, string, count)   file "c:\python27\lib\re.py", line 275, in filter     return sre_parse.expand_template(template, match)   file "c:\python27\lib\sre_parse.py", line 802, in expand_template     raise error, "invalid group reference" sre_constants.error: invalid group reference

what doing wrong here?

r'\1%s'%num becomes equivalent of r'\15, looking group #15 doesn't exist. fix this, replace \1 in replacement \g<1>, way isn't affected digits follow:

temp = re.sub(r'(\w)\d',r'\g<1>%s'%num, temp)

or alternatively, add new digit after performing replacement remove original digit:

temp = '%s%s' % (re.sub(r'(\w)\d', r'\1', temp), num)

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