Numerical error when accessing the rotation angle in quaternion

[shmpwk]

pyquaternion version: 0.9.9, python3 version: 3.8.0

I create a quaternion object explicitly by rotation parameters. (explicitly-by-rotation-parameters). I access the rotation angle like here.

>>> import math
>>> from pyquaternion.quaternion import Quaternion 
>>> Quaternion(axis=[0.0,0.0,1.0], radians=4.0*np.pi).radians
4.440892098500626e-16

I expect that the example outcome is 0.0 (float type) but there seems to be numerical error. Is there any idea to eliminate the numerical error? Does rotation parameter have the range limit?

[Edited] This can be addressed by https://github.com/KieranWynn/pyquaternion/pull/79

[shmpwk]

Another example is when rotating object.

>>> Quaternion(axis=[0.0,0.0,1.0], radians=np.pi/2.0).rotate([0.5,0.5,0.0])
[-0.49999999999999983, 0.5, 0.0]

This is mainly caused by here, which multiply quaternions.