code explanation
Rodrick Brown
rodrick.brown at gmail.com
Mon Jan 14 23:51:40 EST 2013
On Mon, Jan 14, 2013 at 11:38 PM, Steven D'Aprano <
steve+comp.lang.python at pearwood.info> wrote:
> On Mon, 14 Jan 2013 23:00:16 -0500, Rodrick Brown wrote:
>
> > Can someone explain what's going on here.
> >
> > def _build_magic_dispatcher(method):
> > def inner(self, *args, **kwargs):
> > return self.__dict__[method](*args, **kwargs)
> > inner.__name__ = method
> > return inner
> >
> > Thanks.
>
>
> This is a factory function, probably intended to be used as a decorator:
>
> class K:
> @_build_magic_dispatcher
> def something(self, x, y, z): ...
>
> except that it appears to be broken. It seems to be expecting a *string*,
> the name of a method, despite the function parameter claiming to require
> a method itself. So maybe you use it like this:
>
> class K:
> def __init__(self):
> self.parrot = _build_magic_dispatcher("parrot")
>
>
> or something similar. Without seeing the context, it's hard for me to
> tell whether it works or is broken. I suspect it is broken, or useless,
> or both.
>
> So, this factory function seems to take the *name* of a method as
> argument. Then it builds an inner method, which accepts arbitrary
> arguments (args and kwargs), renames the inner method to the name you
> passed as argument, and returns it.
>
>
Thanks Steven, here is the full context of the code. I'm trying to
understand what exactly the author is trying to accomplish here.
import sys
PY3K = sys.version_info >= (3,)
methods = set([
"__iter__",
"__len__",
"__contains__",
"__lt__",
"__le__",
"__eq__",
"__ne__",
"__gt__",
"__ge__",
"__add__",
"__and__",
"__divmod__",
"__floordiv__",
"__lshift__",
"__mod__",
"__mul__",
"__or__",
"__pow__",
"__rshift__",
"__sub__",
"__truediv__",
"__xor__",
])
if PY3K:
methods.add("__next__")
methods.add("__bool__")
else:
methods.add("__div__")
methods.add("__nonzero__")
MAGIC_METHODS = frozenset(methods)
del methods
def _build_magic_dispatcher(method):
def inner(self, *args, **kwargs):
return self.__dict__[method](*args, **kwargs)
inner.__name__ = method
return inner
class stub(object):
_classes_cache = {}
def __new__(cls, **kwargs):
magic_methods_present = MAGIC_METHODS.intersection(kwargs)
if magic_methods_present not in cls._classes_cache:
attrs = dict(
(method, _build_magic_dispatcher(method))
for method in magic_methods_present
)
attrs["__module__"] = cls.__module__
cls._classes_cache[magic_methods_present] = type("stub",
(cls,), attrs)
new_cls = cls._classes_cache[magic_methods_present]
return super(stub, new_cls).__new__(new_cls, **kwargs)
def __init__(self, **kwargs):
self.__dict__.update(kwargs)
> The inner method simply looks up an attribute with the same name, and
> calls it as a function with whatever args and kwargs it gets.
>
>
> Does this help?
>
>
>
> --
> Steven
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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