When handling the return from a web server that dooes
not return the content length(one I wrote) httplib
takes an exception at line 478.

The line of code in question is 
if self.length is not None:

and should probably read
if self.length is not None and self.length != _UNKNOWN:

The problem is that self.length is no longer
initialized to None

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On which version of Python does this occur?

In HEAD, all code paths in begin() lead to self.length being
set to some value or None.

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Here is the version header from running python at the
command line.
Python 2.4 (#1, Feb  3 2005, 08:52:54

In my httplib.py length is initialized to _UNKNOWN which has
the value "UNKNOWN"

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It looks like you're getting a HTTP 0.9 response. In Python
2.4.0, self.length wasn't set in this case, but this bug was
fixed in version 2.4.2.

Closing this as Fixed, if the problem persists with Python
2.4.3 please reopen.