How can I do vector math via Python in Maya?

Python has no built-in vector math calls :( You can see my notes on this here. In Maya however, you have a few solutions to continue to do vector math:

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Method A: Write your own wrappers around the mel vector commands:

import maya.mel as mm
def mvCross(vec1, vec2):
    mVec1 = vec1.__str__().replace("[", "<<").replace("]",">>")
    mVec2 = vec2.__str__().replace("[", "<<").replace("]",">>")
    res = mm.eval("cross(" + mVec1 + ", " + mVec2 + ")")
    return list(res)

vec1 = [0,1,0]
vec2 = [1,0,0]
cross = mvCross(vec1,vec2)
print cross
# [0.0, 0.0, -1.0]

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Method B: Call to maya.OpenMaya, and use API MVector (docs) goodness:

import maya.OpenMaya as om
vec1 = om.MVector(0,1,0)
vec2 = om.MVector(1,0,0)
vec3 = vec1^vec2  # calculate cross product
print vec3.x, vec3.y, vec3.z
# 0.0 0.0 -1.0

• * operator: The dot product of two MVectors.
• ^ operator: The cross product of two MVectors.

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Method C: Write your own Python vector module, or get someone else's:

• I document the math behind some of the basic vector functions here
• Vector : A fairly robust looking 2d vector solution.
• The 2d and 3d vector classes in the gameobjects package (over at Google Code).
• PyGame have contributed Vec2d and Vec3d classes.

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Method D: Get NumPy
http://numpy.scipy.org
You'll need to make sure that the lib is installed where Maya can see it, like here:

C:\Program Files\Autodesk\Maya<version>\Python\lib\site-packages

Example:

import numpy
v1 = (1,2,3)
v2 = (3,2,1)
v3 = numpy.cross (u, v)