On 08/03/2016 23:28, Steven D'Aprano wrote:
On Tue, 8 Mar 2016 10:53 pm, BartC wrote:
Python 2 Python 3
Text mode 'str' 'str'
Binary mode 'bytes' 'str'
That table is incorrect. In Python 2, bytes is just an alias for str:
[steve@ando ~]$ python2.7 -c "print bytes is str"
True
and reading from a file returns a result depending on whether it is opened
in text or binary mode:
[steve@ando ~]$ echo foo > /tmp/junk
[steve@ando ~]$ python2.7 -c "print type(open('/tmp/junk', 'r').read())"
<type 'str'>
[steve@ando ~]$ python2.7 -c "print type(open('/tmp/junk', 'rb').read())"
<type 'str'>
In Python 3, you get bytes in binary mode, and Unicode strings (known
as "str") in text mode:
[steve@ando ~]$ python3 -c "print(type(open('/tmp/junk', 'r').read()))"
<class 'str'>
[steve@ando ~]$ python3 -c "print(type(open('/tmp/junk', 'rb').read()))"
<class 'bytes'>
Here it is in a table form:
-------- -------- --------
Mode Python 2 Python 3
-------- -------- --------
Text bytes text
Binary bytes bytes
-------- -------- --------
That doesn't correspond to your results above. Going with the reported
type of what is read, it would be:
-------- -------- --------
Mode Python 2 Python 3
-------- -------- --------
Text str str
Binary str bytes
-------- -------- --------
Notice the odd-one-out is now the bottom left, not the the top right.
Python will never expand \n to \r\n. But it may translate \r\n to \n.
Well, OK, you might lose bytes with the value 13. That's also bad.
If you pass a file-handle to a function, that function can't just do a
read from that handle without considering whether the file might be in
text or binary mode, or whether it's running under Py2 or Py3.
Why not? file.read() works exactly the same in all four cases.
Didn't you just demonstrate that it can give different results?
It's hard to argue against your statement when I don't understand what
problem you think you have. A concrete example of this "mess" would help.
And I think someone pointed out the difference between 'bytes',
'bytearray' and 'array.array', but I can't find that post at the minute.
Er, yes? Of course there is a differences between those three types. There's
also a difference between list, set and dict. What's your point?
OK, I take it back; if it's not a mess, then it's just confusing!
If someone asked me when I'd use a byte sequence, and when I'd use a
bytearray object, then I wouldn't have a clue.
(Looking it up, it appears than one is mutable, and the other isn't.
This isn't quite the same as the difference between a list and a dict.)
As for array.arrays, those apparently can also be arrays of bytes.
Presumably, mutable. OK. Definitely nothing here that could be tidied up...
--
Bartc
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