Summary¶
seven is a Python 2.6+ compatibility layer for Python 2.5. It allows you to
import Python 2.6 or 2.7 code in a 2.5 interpreter.
It was mainly intended to be used on Google App Engine, before the guys at Google added Python 2.7 support.
The project development is now discontinued, but you are welcome to use it for whatever you might need it.
It is licensed under the MIT licence, except for the lib2to3 code it contains, which in made available under the PSF licence. Those files contain individual licence information, so check the source code for more info.
Basic usage¶
Before importing non-compatible code, you need to start the seven import
hook by calling seven.start():
>>> import seven
>>> seven.start()
>>> import incompatible.modules
>>> seven.stop() # optional
The above will install an import hook and preprocess all modules before
importing them using lib2to3 from the Python 2.7 stdlib. The
installed hook will process all imported python modules until you call
seven.stop(). If you don’t stop it, all imports will be processed.
Import whitelists¶
Preprocessing all imported modules might not always be a good idea, mainly for two reasons. Firs, it comes with a slight performance penalty. Second, more important reason is that exceptions raised in modules that have been processed by the import hook can be really hard to debug. Line numbers are usually wrong, and the filename is not displayed correctly. These things might be improved in the future, but for now it is advised that only the necessary modules be processed.
The following example will only preprocess the modules foo, spam.eggs
and their submodules, foo.* and spam.eggs.*:
>>> seven.start(['foo', 'spam.eggs'])
What gets fixed?¶
Of course, not all fixers have been implemented yet. The following features are
available (without using from __future__ imports):
withstatement (from __future__ import with_statement)- absolute imports (
from __future__ import absolute_imports) - integer division (
from __future__ import division) - class decorators
Class decorators are converted like this:
@decorated
class C:
pass
becomes:
class C:
pass
C = decorated(C)
How to disable logging and pickling?¶
On certain production environments, logging might not be very useful, or
writing files might not be possible (e.g. App Engine). To disable logging or
writing pickle dumps, create a module named sevenconfig and add the log =
False or speedups = False globals (or both). Make sure the module is
importable before importing seven.
What needs to be implemented?¶
The following features do not have fixers yet:
- indented
classdecorators except Exception as e:- advanced string formatting
printas a functionsetliteralsdictandsetcomprehensions- multiple context managers in one
withstatement - etc.