def docstring(self, node):
        if isinstance(node, ast.Expr):
            node = node.value
        if not isinstance(node, ast.Str):
            return (None, None)
        # Computed incorrectly if the docstring has backslash
        doctest_lineno = node.lineno - node.s.count('\n') - 1
        return (node.s, doctest_lineno)