According to PEP 358, a bytes object is used to store a mutable sequence of bytes (0-255), raising if this is not the case.
However, my python 2.7 says otherwise
The bytes
type was introduced in Python 3, but what's being discussed in the PEP is a mutable sequence (bytes
is immutable) which was introduced in Python 2.6 under the name bytearray
.
The PEP clearly wasn't implemented as stated (and it does say that it was partially superseded by PEP 3137) but I think it's only a question of things being renamed, not features missing. In Python 2 bytes
is just an alias for str
to aid forward compatibility and so is a red-herring here.
Example bytearray usage:
>>> a = bytearray([1,2,3])
>>> a[0] = 5
>>> a
bytearray(b'\x05\x02\x03')
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 thestr
type, and it also supports theb''
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 representingABC
; in 2.6,bytes([65, 66, 67])
returns the 12-byte string representing thestr()
of the list.The primary use of
bytes
in 2.6 will be to write tests of object type such asisinstance(x, bytes)
. This will help the2to3
converter, which can’t tell whether 2.x code intends strings to contain either characters or 8-bit bytes; you can now use eitherbytes
orstr
to represent your intention exactly, and the resulting code will also be correct in Python 3.0.
bytes
objects only really exist in Python 3.x. bytes
is an alias for str in Python 2.7. It exists to help writing portable code between Python 2 and 3.