Nicely done :-)
"foo" may come from a library or something, so rather than a decorator we may have to monkey patch it. Unless there is a nicer solution.
Will functools be a good place for something like this?

On Thursday 23 January 2014 01:50 PM, Chris Angelico wrote:

On Thu, Jan 23, 2014 at 7:11 PM, Suresh V. <suresh_vv@yahoo.com> wrote:

On Thursday 23 January 2014 01:22 PM, Chris Angelico wrote:

On Thu, Jan 23, 2014 at 6:20 PM, Suresh V. <suresh_vv@yahoo.com> wrote:

Can we add these two attributes for every function/method where each is a
list of callables with the same arguments as the function/method itself?

Pardon me if this has been discussed before. Pointers to past discussions
(if any) appreciated.

I'm not exactly sure what you're looking for here. What causes a
callable to be added to a function's __before__ list, and/or what will
be done with it?

These are modifiable attributes, so something can be added/deleted from the
__before__ or __after__ lists.

If you mean that they'll be called before and after the function
itself, that can be more cleanly done with a decorator.

Yes. Each item in the list will be called in order immediately before/after
each invocation of the function. This is kinda like decorators, but more
flexible and simpler. Scope for abuse may be higher too :-)

def prepostcall(func):
     def wrapper(*args,**kwargs):
         for f in wrapper.before: f(*args,**kwargs)
         ret = func(*args,**kwargs)
         for f in wrapper.after: f(*args,**kwargs)
         return ret
     wrapper.before = []
     wrapper.after = []
     return wrapper

@prepostcall
def foo(x,y,z):
     return x*y+z

foo.before.append(lambda x,y,z: print("Pre-call"))
foo.after.append(lambda x,y,z: print("Post-call"))

Now just deal with the question of whether the after functions should
be called if the wrapped function throws :)

ChrisA
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