Changes in previous versions¶

Bug fixes¶

• This release expands the future.moves package to include most of the remaining modules that were moved in the standard library reorganization (PEP 3108). (Issue #104)
• This release also removes the broken --doctests_only option from the futurize and pasteurize scripts for now. (Issue #103)

Internal cleanups¶

The project folder structure has changed. Top-level packages are now in a src folder and the tests have been moved into a project-level tests folder.

The following deprecated internal modules have been removed (Issue #80):

• future.utils.encoding and future.utils.six.

Deprecations¶

The following internal functions have been deprecated and will be removed in a future release:

• future.standard_library.scrub_py2_sys_modules
• future.standard_library.scrub_future_sys_modules

Deprecations¶

The following unused internal modules are now deprecated. They will be removed in a future release:

• future.utils.encoding and future.utils.six.

(Issue #80). See here for the rationale for unbundling them.

New features¶

• Docs: Add Cheat Sheet: Writing Python 2-3 compatible code from Ed Schofield’s PyConAU 2014 talk.
• Add newint.to_bytes() and newint.from_bytes(). (Issue #85)
• Add future.utils.raise_from as an equivalent to Py3’s raise ... from ... syntax. (Issue #86)
• Add past.builtins.oct() function.
• Add backports for Python 2.6 of subprocess.check_output(), itertools.combinations_with_replacement(), and functools.cmp_to_key().

Bug fixes¶

• Use a private logger instead of the global logger in future.standard_library (Issue #82). This restores compatibility of the standard library hooks with flask. (Issue #79)
• Stage 1 of futurize no longer renames next methods to __next__ (Issue #81). It still converts obj.next() method calls to next(obj) correctly.
• Prevent introduction of a second set of parentheses in print() calls in some further cases.
• Fix isinstance checks for subclasses of future types. (Issue #89)
• Be explicit about encoding file contents as UTF-8 in unit tests. (Issue #63) Useful for building RPMs and in other environments where LANG=C.
• Fix for 3-argument pow(x, y, z) with newint arguments. (Thanks to @str4d.) (Issue #87)

More robust standard-library import hooks¶

Note: backwards-incompatible change: As previously announced (see Deprecated feature: auto-installation of standard-library import hooks), the import hooks must now be enabled explicitly, as follows:

from future import standard_library
with standard_library.hooks():
    import html.parser
    import http.client
    ...

This now causes these modules to be imported from future.moves, a new package that provides wrappers over the native Python 2 standard library with the new Python 3 organization. As a consequence, the import hooks provided in future.standard_library are now fully compatible with the Requests library.

The functional interface with install_hooks() is still supported for backwards compatibility:

from future import standard_library
standard_library.install_hooks():

import html.parser
import http.client
...
standard_library.remove_hooks()

Explicit installation of import hooks allows finer-grained control over whether they are enabled for other imported modules that provide their own Python 2/3 compatibility layer. This also improves compatibility of future with tools like py2exe.

newobject base object defines fallback Py2-compatible special methods¶

There is a new future.types.newobject base class (available as future.builtins.object) that can streamline Py2/3 compatible code by providing fallback Py2-compatible special methods for its subclasses. It currently provides next() and __nonzero__() as fallback methods on Py2 when its subclasses define the corresponding Py3-style __next__() and __bool__() methods.

This obviates the need to add certain compatibility hacks or decorators to the code such as the @implements_iterator decorator for classes that define a Py3-style __next__ method.

In this example, the code defines a Py3-style iterator with a __next__ method. The object class defines a next method for Python 2 that maps to __next__:

from future.builtins import object

class Upper(object):
    def __init__(self, iterable):
        self._iter = iter(iterable)
    def __next__(self):                 # note the Py3 interface
        return next(self._iter).upper()
    def __iter__(self):
        return self

assert list(Upper('hello')) == list('HELLO')

newobject defines other Py2-compatible special methods similarly: currently these include __nonzero__ (mapped to __bool__) and __long__ (mapped to __int__).

Inheriting from newobject on Python 2 is safe even if your class defines its own Python 2-style __nonzero__ and next and __long__ methods. Your custom methods will simply override those on the base class.

On Python 3, as usual, future.builtins.object simply refers to builtins.object.

past.builtins module improved¶

The past.builtins module is much more compatible with the corresponding builtins on Python 2; many more of the Py2 unit tests pass on Py3. For example, functions like map() and filter() now behave as they do on Py2 with with None as the first argument.

The past.builtins module has also been extended to add Py3 support for additional Py2 constructs that are not adequately handled by lib2to3 (see Issue #37). This includes new execfile() and cmp() functions. futurize now invokes imports of these functions from past.builtins.

surrogateescape error handler¶

The newstr type (future.builtins.str) now supports a backport of the Py3.x 'surrogateescape' error handler for preserving high-bit characters when encoding and decoding strings with unknown encodings.

newlist type¶

There is a new list type in future.builtins that offers .copy() and .clear() methods like the list type in Python 3.

listvalues and listitems¶

future.utils now contains helper functions listvalues and listitems, which provide Python 2-style list snapshotting semantics for dictionaries in both Python 2 and Python 3.

These came out of the discussion around Nick Coghlan’s now-withdrawn PEP 469.

There is no corresponding listkeys(d) function; use list(d) instead.

Tests¶

The number of unit tests has increased from 600 to over 800. Most of the new tests come from Python 3.3’s test suite.

Refactoring of future.standard_library.* -> future.backports¶

The backported standard library modules have been moved to future.backports to make the distinction clearer between these and the new future.moves package.

Backported http.server and urllib modules¶

Alpha versions of backports of the http.server and urllib module from Python 3.3’s standard library are now provided in future.backports.

Use them like this:

from future.backports.urllib.request import Request    # etc.
from future.backports.http import server as http_server

Or with this new interface:

from future.standard_library import import_, from_import

Request = from_import('urllib.request', 'Request', backport=True)
http = import_('http.server', backport=True)

Internal refactoring¶

The future.builtins.types module has been moved to future.types. Likewise, past.builtins.types has been moved to past.types. The only user-visible effect of this is to change repr(type(obj)) for instances of these types. For example:

>>> from future.builtins import bytes
>>> bytes(b'abc')
>>> type(b)
future.types.newbytes.newbytes

Instead of:

>>> type(b)           # prior to v0.12
future.builtins.types.newbytes.newbytes

Bug fixes¶

Many small improvements and fixes have been made across the project. Some highlights are:

• Fixes and updates from Python 3.3.5 have been included in the backported standard library modules.
• Scrubbing of the sys.modules cache performed by remove_hooks() (also called by the suspend_hooks and hooks context managers) is now more conservative.

• The fix_next and fix_reduce fixers have been moved to stage 1 of futurize.
• futurize: Shebang lines such as #!/usr/bin/env python and source code file encoding declarations like # -*- coding=utf-8 -*- are no longer occasionally displaced by from __future__ import ... statements. (Issue #10)
• Improved compatibility with py2exe (Issue #31).
• The future.utils.bytes_to_native_str function now returns a platform-native string object and future.utils.native_str_to_bytes returns a newbytes object on Py2. (Issue #47).
• The backported http.client module and related modules use other new backported modules such as email. As a result they are more compliant with the Python 3.3 equivalents.

Improved compatibility with requests¶

The __exit__ function of the hooks context manager and the remove_hooks function both now remove submodules of future.standard_library from the sys.modules cache. Therefore this code is now possible on Python 2 and 3:

from future import standard_library
standard_library.install_hooks()
import http.client
standard_library.remove_hooks()
import requests

data = requests.get('http://www.google.com')

Previously, this required manually removing http and http.client from sys.modules before importing requests on Python 2.x. (Issue #19)

This change should also improve the compatibility of the standard library hooks with any other module that provides its own Python 2/3 compatibility code.

Note that the situation will improve further in version 0.12; import hooks will require an explicit function call or the hooks context manager.

Conversion scripts explicitly install import hooks¶

The futurize and pasteurize scripts now add an explicit call to install_hooks() to install the standard library import hooks. These scripts now add these two lines:

from future import standard_library
standard_library.install_hooks()

instead of just the first one. The next major version of future (0.12) will require the explicit call or use of the hooks context manager. This will allow finer-grained control over whether import hooks are enabled for other imported modules, such as requests, which provide their own Python 2/3 compatibility code.

futurize script no longer adds unicode_literals by default¶

There is a new --unicode-literals flag to futurize that adds the import:

from __future__ import unicode_literals

to the top of each converted module. Without this flag, futurize now no longer adds this import. (Issue #22)

The pasteurize script for converting from Py3 to Py2/3 still adds unicode_literals. (See the comments in Issue #22 for an explanation.)

past package¶

The python-future project now provides a past package in addition to the future package. Whereas future provides improved compatibility with Python 3 code to Python 2, past provides support for using and interacting with Python 2 code from Python 3. The structure reflects that of future, with past.builtins and past.utils. There is also a new past.translation package that provides transparent translation of Python 2 code to Python 3. (See below.)

One purpose of past is to ease module-by-module upgrades to codebases from Python 2. Another is to help with enabling Python 2 libraries to support Python 3 without breaking the API they currently provide. (For example, user code may expect these libraries to pass them Python 2’s 8-bit strings, rather than Python 3’s bytes object.) A third purpose is to help migrate projects to Python 3 even if one or more dependencies are still on Python 2.

Currently past.builtins provides forward-ports of Python 2’s str and dict objects, basestring, and list-producing iterator functions. In later releases, past.builtins will be used internally by the past.translation package to help with importing and using old Python 2 modules in a Python 3 environment.

Auto-translation of Python 2 modules upon import¶

past provides an experimental translation package to help with importing and using old Python 2 modules in a Python 3 environment.

This is implemented using import hooks that attempt to automatically translate Python 2 modules to Python 3 syntax and semantics upon import. Use it like this:

$ pip3 install plotrique==0.2.5-7 --no-compile   # to ignore SyntaxErrors
$ python3

Then pass in a whitelist of module name prefixes to the past.autotranslate() function. Example:

>>> from past import autotranslate
>>> autotranslate(['plotrique'])
>>> import plotrique

This is intended to help you migrate to Python 3 without the need for all your code’s dependencies to support Python 3 yet. It should be used as a last resort; ideally Python 2-only dependencies should be ported properly to a Python 2/3 compatible codebase using a tool like futurize and the changes should be pushed to the upstream project.

For more information, see Using Python 2-only dependencies on Python 3.

Separate pasteurize script¶

The functionality from futurize --from3 is now in a separate script called pasteurize. Use pasteurize when converting from Python 3 code to Python 2/3 compatible source. For more information, see pasteurize: Py3 to Py2/3.

pow()¶

There is now a pow() function in future.builtins.misc that behaves like the Python 3 pow() function when raising a negative number to a fractional power (returning a complex number).

input() no longer disabled globally on Py2¶

Previous versions of future deleted the input() function from __builtin__ on Python 2 as a security measure. This was because Python 2’s input() function allows arbitrary code execution and could present a security vulnerability on Python 2 if someone expects Python 3 semantics but forgets to import input from future.builtins. This behaviour has been reverted, in the interests of broadening the compatibility of future with other Python 2 modules.

Please remember to import input from future.builtins if you use input() in a Python 2/3 compatible codebase.

Deprecated feature: auto-installation of standard-library import hooks¶

Previous versions of python-future installed import hooks automatically upon importing the standard_library module from future. This has been deprecated in order to improve robustness and compatibility with modules like requests that already perform their own single-source Python 2/3 compatibility.

As of v0.12, importing future.standard_library will no longer install import hooks by default. Instead, please install the import hooks explicitly as follows:

from future import standard_library
standard_library.install_hooks()

And uninstall them after your import statements using:

standard_library.remove_hooks()

Note: This is a backward-incompatible change.

Internal changes¶

The internal future.builtins.backports module has been renamed to future.builtins.types. This will change the repr of future types but not their use.

New context-manager interface to standard_library.hooks¶

There is a new context manager future.standard_library.hooks. Use it like this:

from future import standard_library
with standard_library.hooks():
    import queue
    import configserver
    from http.client import HTTPConnection
    # etc.

If not using this context manager, it is now encouraged to add an explicit call to standard_library.install_hooks() as follows:

from future import standard_library
standard_library.install_hooks()

import queue
import html
import http.client
# etc.

And to remove the hooks afterwards with:

standard_library.remove_hooks()

The functions install_hooks() and remove_hooks() were previously called enable_hooks() and disable_hooks(). The old names are deprecated (but are still available as aliases).

As usual, this feature has no effect on Python 3.

Backported dict type¶

future.builtins now provides a Python 2 dict subclass whose keys(), values(), and items() methods produce memory-efficient iterators. On Python 2.7, these also have the same set-like view behaviour as on Python 3. This can streamline code needing to iterate over large dictionaries. For example:

from __future__ import print_function
from future.builtins import dict, range

squares = dict({i: i**2 for i in range(10**7)})

assert not isinstance(d.items(), list)
# Because items() is memory-efficient, so is this:
square_roots = dict((i_squared, i) for (i, i_squared) in squares.items())

For more information, see dict.

Utility functions raise_ and exec_¶

The functions raise_with_traceback() and raise_() were added to future.utils to offer either the Python 3.x or Python 2.x behaviour for raising exceptions. Thanks to Joel Tratner for the contribution of these. future.utils.reraise() is now deprecated.

A portable exec_() function has been added to future.utils from six.

Bugfixes¶

• Fixed newint.__divmod__
• Improved robustness of installing and removing import hooks in future.standard_library
• v0.10.1: Fixed broken pip install future on Py3

isinstance checks are supported natively with backported types¶

The isinstance function is no longer redefined in future.builtins to operate with the backported int, bytes and str. isinstance checks with the backported types now work correctly by default; we achieve this through overriding the __instancecheck__ method of metaclasses of the backported types.

For more information, see isinstance.

futurize: minimal imports by default¶

By default, the futurize script now only adds the minimal set of imports deemed necessary.

There is now an --all-imports option to the futurize script which gives the previous behaviour, which is to add all __future__ imports and from future.builtins import * imports to every module. (This even applies to an empty __init__.py file.)

Looser type-checking for the backported str object¶

Now the future.builtins.str object behaves more like the Python 2 unicode object with regard to type-checking. This is to work around some bugs / sloppiness in the Python 2 standard library involving mixing of byte-strings and unicode strings, such as os.path.join in posixpath.py.

future.builtins.str still raises the expected TypeError exceptions from Python 3 when attempting to mix it with future.builtins.bytes.

suspend_hooks() context manager added to future.standard_library¶

Pychecker (as of v0.6.1)’s checker.py attempts to import the builtins module as a way of determining whether Python 3 is running. Since this succeeds when from future import standard_library is in effect, this check does not work and pychecker sets the wrong value for its internal PY2 flag is set.

To work around this, future now provides a context manager called suspend_hooks that can be used as follows:

from future import standard_library
...
with standard_library.suspend_hooks():
    from pychecker.checker import Checker

Python 2.6 support¶

future now includes support for Python 2.6.

To run the future test suite on Python 2.6, this additional package is needed:

pip install unittest2

http.server also requires the argparse package:

pip install argparse

Unused modules removed¶

The future.six module has been removed. future doesn’t require six (and hasn’t since version 0.3). If you need support for Python versions before 2.6, six is the best option. future and six can be installed alongside each other easily if needed.

The unused hacks module has also been removed from the source tree.

isinstance() added to future.builtins (v0.8.2)¶

It is now possible to use isinstance() calls normally after importing isinstance from future.builtins. On Python 2, this is specially defined to be compatible with future‘s backported int, str, and bytes types, as well as handling Python 2’s int/long distinction.

The result is that code that uses isinstance to perform type-checking of ints, strings, and bytes should now work identically on Python 2 as on Python 3.

The utility functions isint, istext, and isbytes provided before for compatible type-checking across Python 2 and 3 in future.utils are now deprecated.