[Tutor] __mul__ for different variable types?
I'm a little confused on this one. I have a Vector class that I want to be able to multiply by either another vector or by a single float value. How would I implement this in my override of __mul__ within that class? Do you check the variable type with a stack of if isinstance statements or something? What is the preferred Python way of doing this? - Warren (war...@wantonhubris.com) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] __mul__ for different variable types?
2009/10/4 Warren war...@wantonhubris.com: I'm a little confused on this one. I have a Vector class that I want to be able to multiply by either another vector or by a single float value. How would I implement this in my override of __mul__ within that class? Do you check the variable type with a stack of if isinstance statements or something? What is the preferred Python way of doing this? - Warren (war...@wantonhubris.com) ___ Tutor maillist - tu...@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor I think isinstance is probably the most pythonic way of doing this, and don't forget to add __rmul__ as well, for floats: try: from numbers import Real except NameError: Real = (int, long, float) class Vector(object): #__init__ and other methods ommitted. def __mul__(self, other): self * other if isinstance(other, Vector): # code for Vector * Vector elif isinstance(other, Number): # code for Vector * number else: return NotImplemented def __rmul__(self, other): other * self return self.__mul__(other) Note that I've got no type checking in __rmul__, because if only Vector * Vector has a different value if the terms are swapped, and other * self will use other.__mul__ if other is a Vector. Also note the import at the top: numbers.Real is an Abstract Base Class use for all real number types, introduced in Python 2.6, so simplifies testing types. See http://docs.python.org/library/numbers.html for info. If it's not there, the code demos another feature of isinstance most people don't notice: the type argument can be a sequence of types, so I set Real to a tuple of all the builtin real number types (that I can remember off the top of my head) if the import fails. If you want multiplication to be defined for complex numbers, change all occurances of Real to Number, and add complex to the tuple. -- Rich Roadie Rich Lovely There are 10 types of people in the world: those who know binary, those who do not, and those who are off by one. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] __mul__ for different variable types?
Awesome, Rich, thanks! - Warren (war...@wantonhubris.com) On Oct 4, 2009, at 5:31 PM, Rich Lovely wrote: 2009/10/4 Warren war...@wantonhubris.com: I'm a little confused on this one. I have a Vector class that I want to be able to multiply by either another vector or by a single float value. How would I implement this in my override of __mul__ within that class? Do you check the variable type with a stack of if isinstance statements or something? What is the preferred Python way of doing this? - Warren (war...@wantonhubris.com) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor I think isinstance is probably the most pythonic way of doing this, and don't forget to add __rmul__ as well, for floats: try: from numbers import Real except NameError: Real = (int, long, float) class Vector(object): #__init__ and other methods ommitted. def __mul__(self, other): self * other if isinstance(other, Vector): # code for Vector * Vector elif isinstance(other, Number): # code for Vector * number else: return NotImplemented def __rmul__(self, other): other * self return self.__mul__(other) Note that I've got no type checking in __rmul__, because if only Vector * Vector has a different value if the terms are swapped, and other * self will use other.__mul__ if other is a Vector. Also note the import at the top: numbers.Real is an Abstract Base Class use for all real number types, introduced in Python 2.6, so simplifies testing types. See http://docs.python.org/library/numbers.html for info. If it's not there, the code demos another feature of isinstance most people don't notice: the type argument can be a sequence of types, so I set Real to a tuple of all the builtin real number types (that I can remember off the top of my head) if the import fails. If you want multiplication to be defined for complex numbers, change all occurances of Real to Number, and add complex to the tuple. -- Rich Roadie Rich Lovely There are 10 types of people in the world: those who know binary, those who do not, and those who are off by one. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
