squaternion
)
Simple Quaternions (
Generally I don't need all of the capabilities (or complexity) of quaternion
math libraries. Basically I just need a way to convert between Euler and
Quaternion representations and have a nice way to print them out.
This has basically no imports outside of standard python 3.x libraries.
It should be easier to get on embedded python systems without having to build
numpy
. Also, this tries to be fast by using a frozen class with slots and
where it makes sense, returns tuples
instead of list
s.
Alternatives
This is a basic library that converts between Euler angles and Quaternions. There are other libraries that do so much more listed below ... but I don't need all of that.
 scipy.spatial.transform.Rotation: has everything you could want, with lots of imports

tinyquaternion: appears to be more functional but needs
numpy
 quaternions: another good lightweight quaternion package

pyrr: seems good, integrated with
numpy
Install
pip install squaternion
Usage
from squaternion import Quaternion
# if you know the values you want Quaternion(w, x, y, z), note this is a
# attr frozen class so it is immutable once created
q = Quaternion(1,0,0,0)
# multiplication for scalar (int, double) and with another quaternion
q = Quaternion(1,2,3,4)
q*q => Quaternion(w=28, x=4, y=6, z=8)
3*q => Quaternion(w=3, x=6, y=9, z=12)
q*3.0 => Quaternion(w=3.0, x=6.0, y=9.0, z=12.0)
# Addition and subtraction
q = Quaternion(1,2,3,4)
q+q => Quaternion(w=2, x=4, y=6, z=8)
# numpy can do some things, but it will change the tuple to an array, so you might
# need to transform it back to a quaternion
q = Quaternion(1,2,3,4)
np.dot(q,q) => 30
np.sqrt(np.dot(q,q)) => 5.477225575051661
q/np.sqrt(np.dot(q,q)) => array([0.18257419, 0.36514837, 0.54772256, 0.73029674])
Quaternion(*(q/np.sqrt(np.dot(q,q)))) => Quaternion(w=0.18257418583505536, x=0.3651483716701107, y=0.5477225575051661, z=0.7302967433402214)
# however you typically don't think in 4 dimensions, so create from
# euler angles from_eluer(roll, pitch, yaw), default is radians, but set
# degrees true if giving degrees
q = Quaternion.from_euler(0, 90, 100, degrees=True)
# can get the euler angles back out in degrees (set to True)
e = q.to_euler(degrees=True)
d = q.to_dict()
# iterate through values
for i in q:
print(f"{i}")
# indexing like a namedtuple
z = q[3]
z = q[1]
v = q[3:]
w = q[0]
# class properties
v = q.vector # returns a tuple (x,y,z)
s = q.scalar # returns a double (w)
n = q.normalize # returns unit quaternion
m = q.magnitude # returns the magnitude of the quaternion
a = q.angle # returns angle of rotation in radians
a = q.axis # returns axis of rotation
# useful attr functions
q == q # compare will return True
q != q # will return False
print(q) # pretty print
w = q.w
x = q.x
y = q.y
z = q.z
References
 Wikipedia Convert Between Quaternions and Euler Angles
 Wikipedia Euler Angle Definitions
 Wikipedia Gimbal Lock
MIT License
Copyright (c) 2018 Kevin Walchko
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
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