Does operands order matter for spectral distribution arithmetical operations?

[cuixiaofei]

Question

Hello, I have seen the arithmetical operations available in tutorials.
But today, it can't work well, could you help?

Traceback (most recent call last):
  File "MyColormix.py", line 172, in <module>
    sd_result = (16 * red_sd) + (10 * green_sd) + (12 * blue_sd)
TypeError: unsupported operand type(s) for *: 'int' and 'SpectralDistribution'

float number also can not multiply with SpectralDistribution

[KelSolaar]

Hi @cuixiaofei,

This is a great question! We define various under methods, e.g. colour.SpectralDistribution.__add__ and this is what makes the various arithmetical operations possible, e.g. my_sd + 1. For the builtin type int however, there is no __add__ method that support a colour.SpectralDistribution instance so a TypeError is raised.

Try that instead:

>>> import colour
>>> red_sd = colour.sd_ones()
>>> blue_sd = colour.sd_ones()
>>> sum_sd = (red_sd * 16) + (blue_sd * 10)

Cheers,

Thomas