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The documentation for PyBytes_FromObject states:
.. cfunction:: PyObject* PyBytes_FromObject(PyObject *o)
 Return the bytes representation of object *o* that implements
 the buffer protocol.
However, there exists a special-case for integer object in
PyBytes_FromObject that makes the function return a null-initialized
bytes object. Currently, this is only used for handling `bytes(10)'.
I don't like changing APIs after a stable release, but I believe this
behaviour is error-prone and surprising (and darn right annoying even).
So, I believe the special-case should be made specific to the bytes
constructor.
Thus, here is the fine patch.

Oh, in case you wonder, the added PyUnicode_Check(x) check is to force
PyBytes_FromObject to raise an error when given an empty unicode string
(I will this as a comment in my patch).

+1

+1 from me too; I agree the current API of PyBytes_FromObject is ugly. 
Is there still a need for a separate C function for creating a zero-
initialized bytes object from a Py_ssize_t or a Python integer? It's a 
fairly simple operation (PyBytes_FromStringAndSize + memset), so perhaps 
it doesn't need its own public function.
I'm not sure about the extra PyUnicode_Check: this seems to go against 
Python's philosophy of duck-typing. After all, the empty string *is* an 
iterable all of whose elements are integers. And this check doesn't cover 
other, similar, cases: for example, list('') will still be converted by 
PyBytes_FromObject, while list('123') won't. What's the benefit?
If this check is going to stay, there should probably also be a unit test 
for this behaviour.
Apart from the reservation about the PyUnicode_Check, the patch looks good 
to me. All tests pass on my machine (OS X 10.5) with this patch applied.

Mark Dickinson wrote:
> Is there still a need for a separate C function for creating a zero-
> initialized bytes object from a Py_ssize_t or a Python integer?
What C function are you referring to?
> And this check doesn't cover other, similar, cases: for example, list('')
> will still be converted by PyBytes_FromObject, while list('123') won't.
Well, one is a just empty list and the other a list of strings. I don't see
why converting a empty list to bytes should raise an error. Although I agree
the type check is a bit out of place, I think it will help prevents bugs. 
In addition, PyBytes_FromObject() is documented as equivalent to the
built-in
bytes(). Since calling bytes() with any unicode string raises a TypeError
exception, unless an encoding is specified, I believe PyBytes_FromObject()
should also follow this convention.

> What C function are you referring to?
A currently non-existent one! I was wondering whether the current bytes-
from-integer functionality that PyBytes_FromObject supplies is important 
enough to preserve somehow. I'd guess not.

Committed in r77174. Thank you for reviewing!