Returns all column names and their data types as a list.

        >>> df.dtypes
        [('age', 'int'), ('name', 'string')]

def dtypes(self):
        """Returns all column names and their data types as a list.

        >>> df.dtypes
        [('age', 'int'), ('name', 'string')]
        """
        return [(str(f.name), f.dataType.simpleString()) for f in self.schema.fields]