Re: class factory example needed (long)
Thanks Steven and Kent, both of your suggestions look good to me. I'll try both out and pick one. Gary Gary Ruben wrote: OK, I've managed to get this to work with Rainer's method, but I realised it is not the best way to do it, since the methods are being added by the constructor, i.e. they are instance methods. This means that every time a foo object is created, a whole lot of code is being run. It would be better to do the same thing with class 'static' methods, if this is possible, so that the methods are created just once. Is this possible? Gary -- http://mail.python.org/mailman/listinfo/python-list
Re: class factory example needed (long)
OK, I've managed to get this to work with Rainer's method, but I realised it is not the best way to do it, since the methods are being added by the constructor, i.e. they are instance methods. This means that every time a foo object is created, a whole lot of code is being run. It would be better to do the same thing with class 'static' methods, if this is possible, so that the methods are created just once. Is this possible? Gary Rainer Mansfeld wrote: snip If OTOH you want your foo class to have sqrt, arccos, etc. methods without defining them explicitly, I think you're looking for something like: . import Numeric . . class Foo(object): . def __init__(self, value): . self.value = float(value) . for u in ['sqrt', 'cos', 'tan']: . setattr(self, u, lambda uf=getattr(Numeric, u): . uf(self.value + 42.0)) f = Foo(7) f.sqrt() 7.0 HTH Rainer -- http://mail.python.org/mailman/listinfo/python-list
Re: class factory example needed (long)
Gary Ruben wrote: OK, I've managed to get this to work with Rainer's method, but I realised it is not the best way to do it, since the methods are being added by the constructor, i.e. they are instance methods. This means that every time a foo object is created, a whole lot of code is being run. It would be better to do the same thing with class 'static' methods, if this is possible, so that the methods are created just once. Is this possible? See my comment on the recipe at: http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/389793 STeVe -- http://mail.python.org/mailman/listinfo/python-list
Re: class factory example needed (long)
Gary Ruben wrote: OK, I've managed to get this to work with Rainer's method, but I realised it is not the best way to do it, since the methods are being added by the constructor, i.e. they are instance methods. This means that every time a foo object is created, a whole lot of code is being run. It would be better to do the same thing with class 'static' methods, if this is possible, so that the methods are created just once. Is this possible? Here is a solution using a metaclass: import Numeric class MetaFoo(type): def __init__(cls, name, bases, d): super(MetaFoo, cls).__init__(cls, name, bases, d) for u in ['sqrt', 'cos', 'tan']: setattr(cls, u, lambda self, uf=getattr(Numeric, u): uf(self.value + 42.0)) class Foo(object): __metaclass__ = MetaFoo def __init__(self, value): self.value = float(value) f = Foo(7) print f.sqrt() Kent -- http://mail.python.org/mailman/listinfo/python-list
Re: class factory example needed (long)
Thanks for the very helpful reply Rainer, I thought I couldn't use setattr because I need the syntactic sugar sqrt(f) to work, but with your example code Numeric.sqrt(f) does in fact work correctly. I also need to do a bit more than may be possible with a simple lambda function, but I should be able to sort it out from here with the info you provided, thanks again, Gary Rainer Mansfeld wrote: snip Hi Gary, you want your 'class factory' to change the methods of Numeric, so that they accept foo objects and return foo objects? I've not the slightest idea how to achieve that. If OTOH you want your foo class to have sqrt, arccos, etc. methods without defining them explicitly, I think you're looking for something like: . import Numeric . . class Foo(object): . def __init__(self, value): . self.value = float(value) . for u in ['sqrt', 'cos', 'tan']: . setattr(self, u, lambda uf=getattr(Numeric, u): . uf(self.value + 42.0)) f = Foo(7) f.sqrt() 7.0 HTH Rainer -- http://mail.python.org/mailman/listinfo/python-list
Re: class factory example needed (long)
Gary Ruben wrote: I have a class factory problem. You could say that my main problem is that I don't understand class factories. My specific problem: I have a class with several methods I've defined. To this class I want to add a number of other class methods where the method names are taken from a list. For each list member, I want to build a method having the list member name so that I can override another method of the same name for objects which are instances of this class. Finally, I want my class factory which creates the method to call the overridden method. I'm sure my description is confusing, so I'll try to illustrate it. import Numeric # The Numeric module contains a whole lot of methods which operate on certain number types class foo: this is a number type class def __init__(self, value): self.value = float(value) def __str__(self): . . other methods here . import string ufuncs = string.split( sqrt arccos arccosh arcsin arcsinh arctan arctanh cos cosh tan tanh log10 sin sinh sqrt absolute fabs floor ceil fmod exp log conjugate )# these are the methods from Numeric that I want to override/wrap for my number type for u in ufuncs: I need something here which builds methods called sqrt(), arccos(), etc. An illustrative example of the class methods I want to build with some sort of class factory is def sqrt(self): val = Numeric.sqrt(self.value) return foo(Numeric.sqrt(self.value) + 42) def arccos(self): val = Numeric.arccos(self.value) return foo(Numeric.arccos(self.value) + 42) if __name__ == __main__: a = 9 b = foo(7) print Numeric.sqrt(a) print Numeric.sqrt(b) This would print 3 7 Note that the methods I want to create under program control are all identical in form. In this example they all call the wrapped method with an argument 42 greater than the value of the number. Does anyone have an example where they've done something similar or could help me out with an example? thanks in anticipation, Gary Hi Gary, you want your 'class factory' to change the methods of Numeric, so that they accept foo objects and return foo objects? I've not the slightest idea how to achieve that. If OTOH you want your foo class to have sqrt, arccos, etc. methods without defining them explicitly, I think you're looking for something like: . import Numeric . . class Foo(object): . def __init__(self, value): . self.value = float(value) . for u in ['sqrt', 'cos', 'tan']: . setattr(self, u, lambda uf=getattr(Numeric, u): . uf(self.value + 42.0)) f = Foo(7) f.sqrt() 7.0 HTH Rainer -- http://mail.python.org/mailman/listinfo/python-list
class factory example needed (long)
I have a class factory problem. You could say that my main problem is that I don't understand class factories. My specific problem: I have a class with several methods I've defined. To this class I want to add a number of other class methods where the method names are taken from a list. For each list member, I want to build a method having the list member name so that I can override another method of the same name for objects which are instances of this class. Finally, I want my class factory which creates the method to call the overridden method. I'm sure my description is confusing, so I'll try to illustrate it. import Numeric # The Numeric module contains a whole lot of methods which operate on certain number types class foo: this is a number type class def __init__(self, value): self.value = float(value) def __str__(self): . . other methods here . import string ufuncs = string.split( sqrt arccos arccosh arcsin arcsinh arctan arctanh cos cosh tan tanh log10 sin sinh sqrt absolute fabs floor ceil fmod exp log conjugate )# these are the methods from Numeric that I want to override/wrap for my number type for u in ufuncs: I need something here which builds methods called sqrt(), arccos(), etc. An illustrative example of the class methods I want to build with some sort of class factory is def sqrt(self): val = Numeric.sqrt(self.value) return foo(Numeric.sqrt(self.value) + 42) def arccos(self): val = Numeric.arccos(self.value) return foo(Numeric.arccos(self.value) + 42) if __name__ == __main__: a = 9 b = foo(7) print Numeric.sqrt(a) print Numeric.sqrt(b) This would print 3 7 Note that the methods I want to create under program control are all identical in form. In this example they all call the wrapped method with an argument 42 greater than the value of the number. Does anyone have an example where they've done something similar or could help me out with an example? thanks in anticipation, Gary -- http://mail.python.org/mailman/listinfo/python-list
