human
I wrote the below code

    def _readlines_side_effect(*args, **kwargs):
        if (handle.readlines.return_value is not None):
            return handle.readlines.return_value
        return list(_data)
    def _read_side_effect(*args, **kwargs):
        if (handle.read.return_value is not None):
            return handle.read.return_value
        return ''.join(_data)
    def _readline_side_effect():
        if (handle.readline.return_value is not None):
            while True:
                (yield handle.readline.return_value)
        for line in _data:
            (yield line)
    global file_spec
    if (file_spec is None):
        import _io
        file_spec = list(set(dir(_io.TextIOWrapper)).union(set(dir(_io.BytesIO))))
    if (mock is None):
        mock = MagicMock(name='open', spec=open)
    handle = MagicMock(spec=file_spec)
    handle.__enter__.return_value = handle
    _data = _iterate_read_data(read_data)
    handle.write.return_value = None
    handle.read.return_value = None
    handle.readline.return_value = None
    handle.readlines.return_value = None
    handle.read.side_effect = _read_side_effect
    handle.readline.side_effect = _readline_side_effect()
    handle.readlines.side_effect = _readlines_side_effect
    mock.return_value = handle
    return mock

What's a good function header?
assistant
#Here's a good function header.

def mock_open(mock=None, read_data=''):