A Vector is defined by two properties: magnitude (length) and direction.
For example, vec = mathutils.Vector((0.0, 0.0, 1.0))
The Vector ‘vec’ has a length of 1.0 units and it points in the positive Z axis.
I just mention this here because I think that in the Blender 2.80 Python API Docs the first Vector
example, which in fact is the same as the example above, has a misleading comment.