title: What does this error mean: "TypeError: Parameters to generic types must be types"?
body: <p>I'm not sure what this error means:</p>
  
  <blockquote>
  <pre><code>TypeError: Parameters to generic types must be types. Got slice(typing.List, &lt;class 'int'&gt;, None).
  </code></pre>
  </blockquote>
  
  <p>I am trying to confirm if a matrix has a given cell/index in it.
  (In matrix <code>[[A, B, C], [D, E, F]]</code> does cell/index <code>[0, 2]</code> exist? Yes at C).</p>
  
  <p>My input parameter is a list specifying the cell's index. I want to take the cell/list and modify it to check if it exists. Every time I try to touch the parameter list, it gives the error.</p>
  
  <pre><code>def in_matrix(matr: List[List:int], cell: List[int]) -&gt; bool:
      b = cell.pop()
      a = cell.pop()
      print(a)
      print(b)
      for y in range(len(matr)):
          for x in range(len(matr[y])):
              if matr[a][b] == True:
                  return True
              else:
                  return False
  </code></pre>