the bytes type in python 2.7 and PEP-358

The new bytes type is 3.x only. The 2.x bytes built-in is just an alias to the str type. There is no new type called bytes in 2.x; Just a new alias and literal syntax for str.

Here’s the documentation snippet everybody loves:

Python 2.6 adds bytes as a synonym for
the str type, and it also supports the
b'' notation.

The 2.6 str differs from 3.0’s bytes
type in various ways; most notably,
the constructor is completely
different. In 3.0, bytes([65, 66, 67])
is 3 elements long, containing the
bytes representing ABC; in 2.6,
bytes([65, 66, 67]) returns the
12-byte string representing the str()
of the list.

The primary use of bytes in 2.6 will
be to write tests of object type such
as isinstance(x, bytes). This will
help the 2to3 converter, which can’t
tell whether 2.x code intends strings
to contain either characters or 8-bit
bytes; you can now use either bytes or
str to represent your intention
exactly, and the resulting code will
also be correct in Python 3.0.