Python function returning no value

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")

@thegrinner D:\Python>tbl.py ☺ where you sit daily <chair is in the place where you sit daily — Fla-Hyd
– Fla-Hyd, Commented Jan 28, 2013 at 16:30
The comment suppresses newlines - if you edit your post it will be more clear. — thegrinner
– thegrinner, Commented Jan 28, 2013 at 16:31
D:\Python>tbl.py ☺ where you sit daily <chair is in the place where you sit daily — Fla-Hyd
– Fla-Hyd, Commented Jan 28, 2013 at 16:36

Matt · Accepted Answer · 2013-01-28 16:32:50Z

2

This line:

tblcnt = re.sub(r"<(table.*place)", tblcnv('\1'), rval)

probably doesn't do what you think it should. The call to tblcnv('\1') returns '\1' which is the smiley face you see and then it replaces the first chunk of your string with said smiley face.

answered Jan 28, 2013 at 16:32

Matt

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Comments

isedev · Accepted Answer · 2013-01-28 16:33:09Z

2

When defining tblcnt, you're passing tblcnv('\1'). '\1' is the string containing a single byte with value 0x01. So the result from tblcnv is that same string.

answered Jan 28, 2013 at 16:33

isedev

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1 Comment

Matthias Over a year ago

You might want '\\1' or r'\1'.

bikeshedder · Accepted Answer · 2013-01-28 16:59:34Z

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")

answered Jan 28, 2013 at 16:59

bikeshedder

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2 Comments

Fla-Hyd Over a year ago

it worked like a charm. Thanks a lot for your valuable explanation.

bikeshedder Over a year ago

Would you mind to accept this answer? I would love to see this green tick. Thank you and all the best learning the awesome programming language called python!

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