Hi,
I've taken another stab at #593 and changed the way decorators are
currently evaluated.
http://trac.cython.org/cython_trac/ticket/593
https://github.com/cython/cython/commit/c40ff48f84b5e5841e4e2d2c6dcce3e6494e4c25
We previously had
@deco
def func(): pass
turn into this:
def func(): pass
func = deco(func)
Note how this binds the name more than once and even looks it up in
between, which is problematic in class scopes and some other special cases.
For example, this doesn't work:
class Foo(object):
@property
def x(self):
...
@x.setter
def x(self, value):
...
because "x.setter" is looked up *after* binding the second function "x" to
its method name, thus overwriting the initial property.
The correct way to do it is to create the function object in a temp, pass
it through the decorator call chain, and then assign whatever result this
produces to the method name. This works nicely, but it triggered a crash in
problematic code of another test case, namely "closure_decorators_T478".
That test does this:
def print_args(func):
def f(*args, **kwds):
print "args", args, "kwds", kwds
return func(*args, **kwds)
return f
cdef class Num:
@print_args
def is_prime(self, bint print_factors=False):
...
Now, the problem is that Cython considers "is_prime" to be a method of a
cdef class, although it actually is not. It's only an arbitrary function
that happens to be defined inside of a cdef class body and that happens to
be *called* by a method, namely "f". It now crashes for me because the
"self" argument is not being passed into is_prime() as a C method argument
when called by the wrapper function - and that's correct, because it's not
a method call but a regular function call at that point.
The correct way to fix this is to turn all decorated methods in cdef
classes into plain functions. However, this has huge drawbacks, especially
that the first argument ('self') can no longer be typed as the surrounding
extension type. But, after all, you could do this:
def swap_args(func):
def f(*args):
return func(*args[::-1])
return f
cdef class Num:
@swap_args
def is_prime(arg, self):
...
I'm not sure what to make of this. Does it make sense to go this route? Or
does anyone see a way to make this "mostly" work, e.g. by somehow
restricting cdef classes and their methods? Or should we just add runtime
checks to prevent bad behaviour of decorators?
Stefan
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