title: Please explain -> Vector: in python
body: <p>How to explain -&gt; Vector: in Python</p>
  <p>what does this mean in python</p>
  <pre><code>from typing import List
  Vector = List[float]
  
  def scale(scalar: float, vector: Vector) -&gt; Vector:
      return [scalar * num for num in vector]
  
  # typechecks; a list of floats qualifies as a Vector.
  new_vector = scale(2.0, [1.0, -4.2, 5.4])
  </code></pre>