It's not contrary, it's just convenience. One of the weaknesses in Python (if you can call it that) is that everything is an "object." The classes implementing string, list, and integer simply have methods that respond to those operators and rhs types.

  In [1]: "foo" + 3
  ---------------------------------------------------------------------------
  TypeError                                 Traceback (most recent call last)
  <ipython-input-1-21582e79f06e> in <module>()
  ----> 1 "foo" + 3

  TypeError: cannot concatenate 'str' and 'int' objects

That's because the "special" method "__add__" implemented by the string class will raise TypeError if it gets any object that isn't an instance of a subclass of string.

In a way it is kind of funny to call it, "strongly typed," but it does work. Maybe it should be called, "instancely-typed."