open() ¶

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 Py2.7.
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''
Overview: Easy, clean, reliable Python 2/3 compatibility
Quick-start guide
Cheat Sheet: Writing Python 2-3 compatible code
Imports
What else you need to know
Automatic conversion to Py2/3
Frequently Asked Questions (FAQ)
Standard library incompatibilities
Older interfaces
Changes in previous versions
Licensing and credits
API Reference (in progress)