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Imports

future imports

The imports to include at the top of every Py2/3-compatible module using future are:

from __future__ import (absolute_import, division,
                        print_function, unicode_literals)
from future import standard_library
from future.builtins import *

On Python 3, these import lines have zero effect and zero namespace pollution.

On Python 2, from future import standard_library installs import hooks to allow renamed and moved standard library modules to be imported from their new Py3 locations. See :ref:`standard-library` for more information.

On Python 2, the from future.builtins import * line shadows builtins to provide their Python 3 semantics. (See :ref:`explicit-imports` for the explicit form.)

__future__ imports

For more information about the __future__ imports, which are a standard feature of Python, see the following docs:

These are all available in Python 2.6 and up, and enabled by default in Python 3.x.

Explicit imports

If you prefer explicit imports, the explicit equivalent of the from future.builtins import * line is:

from future.builtins import (filter, map, zip,
                             ascii, chr, hex, input, oct, open,
                             bytes, int, range, round, str, super)

The disadvantage of importing only some of these builtins is that it increases the risk of introducing Py2/3 portability bugs as your code evolves over time.

To understand the details of these functions on Python 2, see the docs for these modules:

  • future.builtins
  • future.builtins.iterators
  • future.builtins.misc
  • future.builtins.backports

The internal API is currently as follows:

from future.builtins.iterators import filter, map, zip
from future.builtins.misc import ascii, chr, hex, input, oct, open
from future.builtins.backports import bytes, int, range, round, str, super

(Please note that this internal API is evolving and may not be stable between different versions of future.)

Obsolete Python 2 builtins

Twelve Python 2 builtins have been removed from Python 3. To aid with porting code to Python 3 module by module, you can use the following import to cause a NameError exception to be raised on Python 2 as on Python 3 when any of the obsolete builtins is used:

from future.builtins.disabled import *

This is equivalent to:

from future.builtins.disabled import (apply, cmp, coerce, execfile,
                             file, long, raw_input, reduce, reload,
                             unicode, xrange, StandardError)

Running futurize over code that uses these Python 2 builtins replaces them with their Python 3 equivalents (which work on Py2 as well using future imports.)