How to do this in Python? - A "gotcha"

[Jim Garrison]

Jim Garrison wrote:
> Luis Zarrabeitia wrote:
>> On Tuesday 17 March 2009 06:04:36 pm Jim Garrison wrote:
>> with open(filename, "rb") as f:
>>     for buf in iter(lambda: f.read(1000),''):
>>         do_something(buf)
> 
> This is the most pythonic solution yet.
> 
> Thanks to all the responders who took time to ponder this seemingly
> trivial question.  I learned a lot about the Python mind-set.

I just tried the code as given above and it results in an infinite loop.

Since f.read() returns a byte string when in binary mode, the sentinel
has to be b''.  Is there a value that will compare equal to both '' and b''?

It's a shame the iter(o,sentinel) builtin does the
comparison itself, instead of being defined as iter(callable,callable)
where the second argument implements the termination test and returns a
boolean.  This would seem to add much more generality... is
it worthy of a PEP?