Question

i am not able to figure out why the below two print statements gives different
results. can any one please explain me? i am just giving a small sample example. in the first print statement table is getting replaced by a special character and the second one gives correct one.

import re  

def tblcnv( str ):  
    rtval = re.sub("table", "chair", str)  
    return rtval  

rval = "<table is in the place where you sit daily "  
tblcnt = re.sub(r"<(table.*place)", tblcnv('\1'), rval)  

print tblcnt  
print tblcnv("<table is in the place where you sit daily")

Answer 1

According to the re.sub manual it takes a function which “is called for every non-overlapping occurrence of pattern”. As those occurrences are actually match objects you are best of using a simple lambda expression which extracts the group(1) of the match objects and passes it to your tblcnv function.

import re

def tblcnv( str ):  
    rtval = re.sub("table", "chair", str)  
    return rtval  

rval = "<table is in the place where you sit daily "  
tblcnt = re.sub(r"<(table.*place)", lambda m: tblcnv(m.group(1)), rval)  

print tblcnt  
print tblcnv("<table is in the place where you sit daily")