deriving from complex

[Scott David Daniels]

Schüle Daniel wrote:
> I am trying to customize the handling of complex numbers
> what I am missing is a builtin possibility to create
> complex numbers in polar coordinates.... I wrote...:
>  >>> def polar(r,arg):
> ...     re, im = r*cos(arg), r*sin(arg)
> ...     return re + im*1j
> then I tried to extend this to a class
>  >>> class Complex(complex):
> ...     def __init__(self,x,y,polar=False):
> ...             if not polar:
> ...                     self.re, self.im = x,y
> ...             else:
> ...                     self.re, self.im = x*cos(y), x*sin(y)

What you are missing is that complex is an immutable type.
You need to fiddle with __new__, not __init__.

     class Complex(complex):
         def __new__(class_, x, y=0.0, polar=False):
             if polar:
                 return complex.__new__(class_, x * cos(y), x * sin(y))
             else:
                 return complex.__new__(class_, x, y)

Which will produce instances of Complex, or:

     class Complex(complex):
         def __new__(class_, x, y=0.0, polar=False):
             if polar:
                 return complex(x * cos(y), x * sin(y))
             else:
                 return complex(class_, x, y)

Which will produce instances of complex.

--Scott David Daniels
scott.daniels at acm.org