def _fields(isu):
    """Returns field names of Issue object."""
    no_method = lambda x: not callable(getattr(isu.fields, x))
    no_magic = lambda x: not x.startswith('_')
    no_constant = lambda x: not x[0].isupper()
    return filter(lambda x: no_magic(x) and no_method(x) and no_constant(x),
        dir(isu.fields))
