Introduction¶
aspectlib provides two core tools to do AOP: Aspects and a weaver.
The aspect¶
An aspect can be created by decorating a generator with an Aspect
. The generator yields advices -
simple behavior changing instructions.
An Aspect
instance is a simple function decorator. Decorating a function with an aspect will change
the function’s behavior according to the advices yielded by the generator.
Example:
@aspectlib.Aspect
def strip_return_value():
result = yield aspectlib.Proceed
yield aspectlib.Return(result.strip())
@strip_return_value
def read(name):
return open(name).read()
Advices¶
You can use these advices:
Proceed
orNone
- Calls the wrapped function with the default arguments. The yield returns the function’s return value or raises an exception. Can be used multiple times (will call the function multiple times).Proceed
(*args, **kwargs)
- Same as above but with different arguments.Return
- Makes the wrapper returnNone
instead. Ifaspectlib.Proceed
was never used then the wrapped function is not called. After this the generator is closed.Return
(value)
- Same as above but returns the givenvalue
instead ofNone
.raise exception
- Makes the wrapper raise an exception.
The weaver¶
Patches classes and functions with the given aspect. When used with a class it will patch all the methods. In AOP parlance these patched functions and methods are referred to as cut-points.
Returns a Rollback
object that can be used a context manager.
It will undo all the changes at the end of the context.
Example:
@aspectlib.Aspect
def mock_open():
yield aspectlib.Return(StringIO("mystuff"))
with aspectlib.weave(open, mock_open):
assert open("/doesnt/exist.txt").read() == "mystuff"
You can use aspectlib.weave()
on: classes, instances, builtin functions, module level functions, methods,
classmethods, staticmethods, instance methods etc.