Re: function factory question: embed current values of object attributes
Terry Reedy wrote: You are now describing a function closure. Here is an example that might help. It does. Thanks, Alan -- http://mail.python.org/mailman/listinfo/python-list
Re: function factory question: embed current values of object attributes
Gabriel Genellina wrote: If you want a frozen function (that is, a function already set-up with the parameters taken from the current values of x.a, x.b) use functools.partial: OK, that's also a nice idea. Thanks! Alan -- http://mail.python.org/mailman/listinfo/python-list
function factory question: embed current values of object attributes
I have a class `X` where many parameters are set at instance initialization. The parameter values of an instance `x` generally remain unchanged, but is there way to communicate to a method that it depends only on the initial values of these parameters (and does not need to worry about any changes)? The behavior of method `m` depends on these parameter values. It turns out `m` gets called a lot, which means that the pameter values are accessed over and over (self.p0, self.p1, etc). I would like to manufacture a function equivalent to the method that simply uses fixed values (the values at the time it is manufactured). I do not care if this function is attached to `x` or not. I have a feeling that I am turning something simple into something complex, perhaps for lack of an afternoon coffee or lack of CS training. Suggestions appreciated. Alan Isaac -- http://mail.python.org/mailman/listinfo/python-list
Re: function factory question: embed current values of object attributes
Alan Isaac wrote: I have a class `X` where many parameters are set at instance initialization. The parameter values of an instance `x` generally remain unchanged, 'Parameters' are the function local names in the header that get bound to argument objects when the function is called. What you are describing are 'attributes'. but is there way to communicate to a method that it depends only on the initial values of these parameters (and does not need to worry about any changes)? In the terms stated, no. The behavior of method `m` depends on these parameter values. It turns out `m` gets called a lot, which means that the pameter values are accessed over and over (self.p0, self.p1, etc). I would like to manufacture a function equivalent to the method that simply uses fixed values (the values at the time it is manufactured). You are now describing a function closure. Here is an example that might help. def f_maker(a1, a2): def _(b): return a1*b + a2 return _ class C: def __init__(self, attr1, attr2): self.attr1 = attr1 self.attr2 = attr2 self.f = f_maker(attr1, attr2) c = C(2,3) print(*(c.f(i) for i in range(5))) # 3 5 7 9 11 Having f use both initial and 'current' attribute values would be a bit trickier ;-) Terry Jan Reedy -- http://mail.python.org/mailman/listinfo/python-list
Re: function factory question: embed current values of object attributes
En Fri, 20 Feb 2009 16:49:21 -0200, Alan Isaac ais...@american.edu escribió: I have a class `X` where many parameters are set at instance initialization. The parameter values of an instance `x` generally remain unchanged, but is there way to communicate to a method that it depends only on the initial values of these parameters (and does not need to worry about any changes)? The behavior of method `m` depends on these parameter values. It turns out `m` gets called a lot, which means that the pameter values are accessed over and over (self.p0, self.p1, etc). I would like to manufacture a function equivalent to the method that simply uses fixed values (the values at the time it is manufactured). I do not care if this function is attached to `x` or not. Not automatically; but you could refactor the method to call an external function with arguments: class X(...): ... def foo(self): c = self.a + self.b return c Rewrite the method as: def foo(self): return _foo(self.a, self.b) and define _foo outside the class: def _foo(a, b): c = a + b return c If you want a frozen function (that is, a function already set-up with the parameters taken from the current values of x.a, x.b) use functools.partial: x = X() frozen_foo = functools.partial(_foo, a=x.a, b=x.b) frozen_foo() # equivalent to x.foo() at the time it was defined But if you call this in a loop, perhaps it's enough to assign x.a, x.b to local variables and call _foo with those arguments. -- Gabriel Genellina -- http://mail.python.org/mailman/listinfo/python-list
