open()ΒΆ
The Python 3 builtin open()
function for opening files returns file
contents as (unicode) strings unless the binary (b
) flag is passed, as in:
open(filename, 'rb')
in which case its methods like read()
return Py3 bytes
objects.
On Py2 with future
installed, the builtins
module provides an
open
function that is mostly compatible with that on Python 3 (e.g. it
offers keyword arguments like encoding
). This maps to the open
backport
available in the standard library io
module on Py2.6 and Py2.7.
One difference to be aware of between the Python 3 open
and
future.builtins.open
on Python 2 is that the return types of methods such
as read()
from the file object that open
returns are not
automatically cast from native bytes or unicode strings on Python 2 to the
corresponding future.builtins.bytes
or future.builtins.str
types. If you
need the returned data to behave the exactly same way on Py2 as on Py3, you can
cast it explicitly as follows:
from __future__ import unicode_literals
from builtins import open, bytes
data = open('image.png', 'rb').read()
# On Py2, data is a standard 8-bit str with loose Unicode coercion.
# data + u'' would likely raise a UnicodeDecodeError
data = bytes(data)
# Now it behaves like a Py3 bytes object...
assert data[:4] == b'\x89PNG'
assert data[4] == 13 # integer
# Raises TypeError:
# data + u''