Decorator and context manager from a single API (Python)

2010-06-27T15:15:01-07:00

Python recipe 577273 by Michael Foord (contextmanager, context_manager, decorator, decorators, with, with_statement). Revision 12.

Create objects that act as both context managers and as decorators, and behave the same in both cases.

Works with Python 2.4 - 2.7 and Python 3. The tests require unittest2 or Python 3.2 to run. (And because the tests use the with statement they won't work with Python 2.4.)

Example:

from contextdecorator import ContextDecorator

class mycontext(ContextDecorator):

    def __init__(self, *args):
        """Normal initialiser"""

    def before(self):
        """
        Called on entering the with block or starting the decorated function.

        If used in a with statement whatever this method returns will be the
        context manager.
        """

    def after(self, *exc):
        """
        Called on exit. Arguments and return value of this method have
        the same meaning as the __exit__ method of a normal context
        manager.
        """

Both before and after methods are optional (but providing neither is somewhat pointless). See the tests for more usage examples.

Total Ordering: Class Decorator for Filling in Rich Comparison Methods When Only One is Implemented (Python)

2008-10-28T11:54:42-07:00

Python recipe 576529 by Michael Foord (class_decorator, comparison, decorator, ordering, sorting). Revision 5.

total_ordering and force_total_ordering are class decorators for Python 2.6 & Python 3.

They provides all the rich comparison methods on a class by defining any one of '__lt__', '__gt__', '__le__', '__ge__'.

total_ordering fills in all unimplemented rich comparison methods, assuming at least one is implemented. __lt__ is taken as the base comparison method on which the others are built, but if that is not available it will be constructed from the first one found.

force_total_ordering does the same, but having taken a comparison method as the base it fills in all the others - this overwrites additional comparison methods that may be implemented, guaranteeing consistent comparison semantics.

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Decorator and context manager from a single API (Python)

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