[Python-Dev] PEP 461 - Adding % and {} formatting to bytes (original) (raw)

Neil Schemenauer nas at arctrix.com
Wed Jan 15 17:27:32 CET 2014

Neil Schemenauer <nas at arctrix.com> wrote:

We should use duck-typing and that means a special method, I think. We could introduce a new one but bytes looks like it can work. Otherwise, maybe ascii is a good name.

I poked around the Python 3 source. Using bytes has some downsides, e.g. the following would happen:

>>> bytes(12)
b'12'

Perhaps that's a little too ASCII-centric. OTOH, UTF-8 seems to be winning the encoding war and so the above could be argued as reasonable behavior. I think forcing people to explicitly choose an encoding for str objects will be sufficient to avoid the bytes/str mess we have in Python 2.

Unfortunately, that change conflicts with the current behavior:

>>> bytes(12)
b'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'

Would it be too disruptive to change that? It doesn't appear to be too useful and we could do it using a keyword argument, e.g.:

bytes(size=12)

I notice something else surprising to me:

>>> class Test(object):
...     def __bytes__(self):
...         return b'test'
...
>>> with open('test', 'wb') as fp:
...     fp.write(Test())
...
Traceback (most recent call last):
  File "<stdin>", line 2, in <module>
TypeError: 'Test' does not support the buffer interface

I'd expect that to write b'test' to the file, not raise an error.

Regards,

Neil

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