n``, ``_replace_booleans``, and
        ``_replace_locals``.

    Returns
    -------
    str
        Valid Python source code

    Notes
    -----
    The `f` parameter can be any callable that takes *and* returns input of the
    form ``(toknum, tokval)``, where ``toknum`` is one of the constants from
    the ``tokenize`` module and ``tokval`` is a string.
    z