input: Write a function to create a Python class called `Vector` to represent a 3-dimensional vector with methods to support vector addition and subtraction. Include methods to print the vector and assert statements to verify the correctness of the methods.
  assert v1.x == 1
  assert v1.y == 2
  assert v1.z == 3
  
  v2 = v1.addVec(Vector(1, 1, 1))
  assert v2.x == 2
  assert v2.y == 3
  assert v2.z == 4
  
  v3 = v1.subVec(Vector(1, 1, 1))
  assert v3.x == 0
  assert v3.y == 1
  assert v3.z == 2
  
  v4 = v1.addVec(Vector(0, 0, 0))
  assert v4.x == 1
  assert v4.y == 2
  assert v4.z == 3
  
  v5 = v1.subVec(Vector(0, 0, 0))
  assert v5.x == 1
  assert v5.y == 2
  assert v5.z == 3
  
  v6 = v1.addVec(Vector(-1, -2, -3))
  assert v6.x == 0
  assert v6.y == 0
  assert v6.z == 0
output: class Vector:
      def __init__(self, x, y, z):
          self.x = x
          self.y = y
          self.z = z
  
      def addVec(self, other):
          return Vector(self.x + other.x, self.y + other.y, self.z + other.z)
  
      def subVec(self, other):
          return Vector(self.x - other.x, self.y - other.y, self.z - other.z)