Python-Future

Common errors

Warnings

Install

Install compatibility verified last tested: 2026-05-12

Imports

• Builtins
  wrong

  from future.builtins import *

  correct

  from builtins import (bytes, dict, int, list, object, range, str,
                         ascii, chr, hex, input, next, oct, open, pow,
                         round, super, filter, map, zip)

  While `future.builtins` exists, the recommended pattern for Python 2/3 compatibility is `from builtins import ...` as it directly maps to Python 3 builtins on Py2 and has no effect on Py3. The wildcard `*` is shown in some examples for brevity but explicit imports are generally preferred.

• StandardLibraryAliases
  wrong

  import urllib.parse  # Directly on Py2 without aliases

  correct

  from future.standard_library import install_aliases
  install_aliases()

  This function makes Python 3-style standard library imports (e.g., `urllib.parse`, `queue`) available on Python 2 by modifying `sys.modules` and other mechanisms.

• __future__ imports

  from __future__ import (absolute_import, division, print_function, unicode_literals)

  These are built-in Python future statements crucial for enabling Python 3 behavior in Python 2. `future`'s tools and runtime patches complement these.

• past.builtins

  from past.builtins import basestring, unicode

  Provides Python 2-specific builtins (like `basestring` or `unicode` type) on Python 3 for modules that explicitly need them, typically during module-by-module migration.

Quickstart verified last tested: 2026-04-23

To write new code compatible with both Python 2 (2.6+) and Python 3 (3.3+), start each module with the essential `__future__` imports and `from builtins import *`. Then call `install_aliases()` to ensure standard library modules are correctly mapped. This allows writing predominantly Python 3-style code that runs on both versions.

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

# Now write Python 3 code that runs on both Py2 and Py3
print("Hello, world!")

def divide(a, b):
    return a / b # Will use float division even on Python 2

my_dict = {'a': 1, 'b': 2}
print(list(my_dict.keys())) # dict.keys() returns a view (iterable) on Py2 with future installed

# Example of Python 3 library name working on Py2
import urllib.request
print(urllib.request.urlopen('http://example.com').getcode())