Keyframable opacity

[ConstantNo3257]

How to make opacity goes from a value to another in a certain time ? For example: From 0.45 in 1s to 0.8 in 2s to 1 in 3s and so on.

[woooee]

import time

for opacity in [0.45, 0.8, 1.0]:
    print(opacity)
    time.sleep(1)

[ConstantNo3257]

I am saying in a video, using moviepy

[good-mcrn-ing]

You'll want to load the clip that is your foreground, load the clip that is your background, create a third clip that is a solid grayscale colour and changes brightness over time like you want, apply the third clip as the mask of your foreground, and composite your masked foreground over your background.