the bytes type in python 2.7 and PEP-358
Question:
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
>>> bytes([1,2,3])
'[1, 2, 3]'
>>> bytes([280])
'[280]'
>>> bytes is str
True
>>> bytes
<type 'str'>
Does anyone have a clue on the reason why the PEP is declared Final, but the implementation does not conform ?
Answers:
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.
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.
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The PEP clearly wasn’t implemented as stated (and it does say that it was partially superseded by PEP 3137) but I think it’s only a question of things being renamed, not features missing.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'x05x02x03')
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
>>> bytes([1,2,3])
'[1, 2, 3]'
>>> bytes([280])
'[280]'
>>> bytes is str
True
>>> bytes
<type 'str'>
Does anyone have a clue on the reason why the PEP is declared Final, but the implementation does not conform ?
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.
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
bytesas a synonym for
thestrtype, and it also supports the
b''notation.The 2.6
strdiffers 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
bytesin 2.6 will
be to write tests of object type such
asisinstance(x, bytes). This will
help the2to3converter, which can’t
tell whether 2.x code intends strings
to contain either characters or 8-bit
bytes; you can now use eitherbytesor
strto represent your intention
exactly, and the resulting code will
also be correct in Python 3.0.
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'x05x02x03')