Since #29463, it is no longer obvious how to get the line number of a docstring in the AST:

    import ast

    x = ast.parse('''\
    def foo():
        """This is a docstring."""
    ''')

    # In Python 3.6, the docstring and line number would be:
    print(x.body[0].body[0].value.s)
    print(x.body[0].body[0].value.lineno)

    # In Python 3.7, I don't know what the equivalent would be.
    print(x.body[0].docstring)
    # Line number?

We use this feature in pyflakes (https://github.com/PyCQA/pyflakes/issues/271).