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b'abc'.partition(':') raises a confusing TypeError('expected an object with the buffer interface'): what is a buffer? what is the buffer interface?
The error comes from PyObject_AsCharBuffer() which is used by:
 - bytes methods: partition, rpartition, find, index, rfind, rindex, count, translate, replace, startswith, endswith
 - complex(): raise a better but incomplete error message on error ("complex() arg is not a string"), incomplete because number is not mentionned
 - float(): raise a better error message on error ("float() argument must be a string or a number")
 - PyArg_Parse*() with the "e" format -> posix.spawnvpe(), imp.load_compiled(), imp.load_source(), imp.load_package()
The error message should be changed to something mentioning classic Python terms. Eg. TypeError("expected bytes, bytearray or buffer compatible object").

See also #6780.

> complex(): raise a better but incomplete error message on error
> ("complex() arg is not a string"), incomplete because number is not
> mentionned
Fixed by r86977.

Victor, I think you attached msg123266 to the wrong issue.

+1 to Victor's proposal ("expected bytes, bytearray or buffer compatible object").

Looking at object.h the buffer interface is defined as 
/* buffer interface */
typedef struct bufferinfo {
 void *buf;
 PyObject *obj; /* owned reference */
 Py_ssize_t len;
 Py_ssize_t itemsize; /* This is Py_ssize_t so it can be
 pointed to by strides in simple case.*/
 int readonly;
 int ndim;
 char *format;
 Py_ssize_t *shape;
 Py_ssize_t *strides;
 Py_ssize_t *suboffsets;
 Py_ssize_t smalltable[2]; /* static store for shape and strides of
 mono-dimensional buffers. */
 void *internal;
} Py_buffer;
typedef int (*getbufferproc)(PyObject *, Py_buffer *, int);
typedef void (*releasebufferproc)(PyObject *, Py_buffer *);
typedef struct {
 getbufferproc bf_getbuffer;
 releasebufferproc bf_releasebuffer;
} PyBufferProcs;
The code that's throwing that error looks like
if (pb == NULL || pb->bf_getbuffer == NULL) {
 PyErr_SetString(PyExc_TypeError,
 "expected an object with the buffer interface");
I would argue that the error message gives appropriate information because it is expecting the object to have a bf_getbuffer member.
Maybe the friendly error message is best handled at a higher level?

+1 to Antoine’s +1.

New changeset 7ed75bb4f37c by Victor Stinner in branch 'default':
Close #10616: mention bytes and bytearray in PyObject_AsCharBuffer() error
http://hg.python.org/cpython/rev/7ed75bb4f37c