title: Change type of member parameter for python type hint
body: <p>I have a code like this:</p>
  
  <pre><code>class A:
      def __init__(self, a: int) -&gt; None:
          self.a: int = a
  
  
  class B(A):
      def __init__(self, a: float) -&gt; None:
          self.a: float = a
  </code></pre>
  
  <p>The problem is that self.a changes from type <em>int</em> in the base class, A, to <em>float</em> in class B. mypy gives me this error:</p>
  
  <pre><code>typehintancestor.py:8: error: Incompatible types in assignment (expression has type "float", variable has type "int")
  </code></pre>
  
  <p>(Line 8 is the last line)</p>
  
  <p>Is this a bug in mypy or should I change the implementation of class B?</p>