[Python-bugs-list] [ python-Bugs-599757 ] sub[n] not working as expected.

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Bugs item #599757, was opened at 2002-08-24 22:14
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Category: Regular Expressions
Group: Python 2.2.1
>Status: Closed
>Resolution: Invalid
Priority: 5
Submitted By: Travis Shirk (nicfit)
Assigned to: Fredrik Lundh (effbot)
Summary: sub[n] not working as expected.

Initial Comment:
I'm running into what looks to be a bug in the python
2.2 re module.
These examples should demonstrate the problem.

Using Python 1.5.2:
import re;
data =
"\xFF\x00\xE0\xD3\xD3\xE4\x95\xFF\x00\x00\x11\xFF\x00\xF5"
data1 =
re.compile(r"\xFF\x00([\xE0-\xFF])").sub(r"\xFF\1", data);
print data1
'\377\340\323\323\344\225\377\000\000\021\377\365'


This output is exactly what I expect, but now see what
happens in 
2.2.1:
import re;
data =
"\xFF\x00\xE0\xD3\xD3\xE4\x95\xFF\x00\x00\x11\xFF\x00\xF5"
data1 =
re.compile(r"\xFF\x00([\xE0-\xFF])").sub(r"\xFF\1", data);
print data1
'\xFF\xe0\xd3\xd3\xe4\x95\xff\x00\x00\x11\xFF\xf5'

I like the hex output over the octal in 1.5, but the
substitution is
clearly wrong.  Notice each spot containing "\" in the
last result.


----------------------------------------------------------------------

>Comment By: Peter Schneider-Kamp (nowonder)
Date: 2002-08-27 16:22

Message:
Logged In: YES 
user_id=14463

The substitution is correct. Notice that the r"..." raw
string given to sub in this example has length 6, not length
3! As you can see from the case, \xFF is a string of length
4 and has no close relationship to the singleton string \xff.

If you use .sub("\xFF\1", data) instead you will achieve
the desired result.

Note that the raw string passed to re.compile() also does
not contain the character \xff itself, but as described in
the documentation, re is able to parse the \xHH-style
character escapes.

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