[Tutor] __mul__ for different variable types?
warren at wantonhubris.com
Sun Oct 4 23:44:31 CEST 2009
Awesome, Rich, thanks!
(warren at wantonhubris.com)
On Oct 4, 2009, at 5:31 PM, Rich Lovely wrote:
> 2009/10/4 Warren <warren at 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
>> 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
>> (warren at wantonhubris.com)
>> Tutor maillist - Tutor at python.org
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> I think isinstance is probably the most pythonic way of doing this,
> and don't forget to add __rmul__ as well, for floats:
> 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
> 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.
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