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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _isinstance(expr, classname):
 """Check whether `expr` is an instance of the class with name `classname` This is like the builtin `isinstance`, but it take the `classname` a string, instead of the class directly. Useful for when we don't want to import the class for which we want to check (also, remember that printer choose rendering method based on the class name, so this is totally ok) """

        for cls in type(expr).__mro__:
            if cls.__name__ == classname:
                return True
        return False