Python计算三维矢量幅度的方法

from numpy import *
from math import *
a=(['x','y','z'])
sum_com=0
for i in range(3):
  y=input("Enter %s component:"%a[i])
  m=y**2
  sum_com += m
magnitude=sqrt(sum_com)
print "The magnitude of vector is %s"%magnitude