Blender python exemple how to create a 90 degree vector from a current vector

create_square_vector_from_another

import bpy
from bpy import context as C
from bpy import data as D
from mathutils import Vector
from math import sqrt

def VectorLength(size, A, B):
    '''
    Calculate the vector lenght
    return the coefficient to multiply this vector
    to have a vector of the size given in paramerter
    '''
    Vlength = sqrt((A[0] - B[0])**2 + (A[1] - B[1])**2 + (A[2] - B[2])**2)
    return (size / Vlength)


#to test, create 3 object named as follow and place foo and bar in space
foo = D.objects['foo'].location
bar = D.objects['bar'].location

#middle location between 2 vector is calculated by adding the two vector and divide by two
mid = (foo + bar) / 2

#between = vector from foo to bar (invert the orperators to get negative vector)
between = foo - bar


#create a generic Up vector (on Y or Z)
up = Vector([0,1.0,0])

#the cross product return a 90 degree Vector
new = Vector.cross(up, between)
'''
####cross product also accessible throuh Numpy module:
###import numpy as np
###new = np.cross(up, between)
###new = Vector(new)
'''

#position of the point in space is found by adding the new vector to the mid location
#but the lenght is according to original foo->bar vector
perpendicular = mid + new
C.scene.cursor_location = perpendicular

#get the coefficient to multiply the new vector to get the same direction bu size 1
coeff = VectorLength(1, mid, perpendicular)

#print ('perp', perpendicular, '\ncoeff', coeff)

#position the point in space by adding the new vector multiplied by coeff value to get wanted lenght
C.scene.cursor_location = mid + (new * coeff)