> This type should exist only at compile time.

But then after doing "x = 5j", "-0.0 + 5j" and "-0.0 + x" would have different values.  Yuck!

> repr() (and str()) should keep zero real part if imaginary part is negative and output period if real part is zero

Sorry, I don't see how this helps.  What do you want the repr of (for example) "complex(-0.0, 5.0)" to be, and why?  What about the cases with 0 in the imaginary part?