Function mock_open

Lib/unittest/mock.py:2971–3054

A helper function to create a mock to replace the use of `open`. It works for `open` called directly or used as a context manager. The `mock` argument is the mock object to configure. If `None` (the default) then a `MagicMock` will be created for you, with the API limited to me

(mock=None, read_data='')

def mock_open(mock=None, read_data=''):
    """
    A helper function to create a mock to replace the use of `open`. It works
    for `open` called directly or used as a context manager.

    The `mock` argument is the mock object to configure. If `None` (the
    default) then a `MagicMock` will be created for you, with the API limited
    to methods or attributes available on standard file handles.

    `read_data` is a string for the `read`, `readline` and `readlines` of the
    file handle to return.  This is an empty string by default.
    """
    _read_data = _to_stream(read_data)
    _state = [_read_data, None]

    def _readlines_side_effect(*args, **kwargs):
        if handle.readlines.return_value is not None:
            return handle.readlines.return_value
        return _state[0].readlines(*args, **kwargs)

    def _read_side_effect(*args, **kwargs):
        if handle.read.return_value is not None:
            return handle.read.return_value
        return _state[0].read(*args, **kwargs)

    def _readline_side_effect(*args, **kwargs):
        yield from _iter_side_effect()
        while True:
            yield _state[0].readline(*args, **kwargs)

    def _iter_side_effect():
        if handle.readline.return_value is not None:
            while True:
                yield handle.readline.return_value
        for line in _state[0]:
            yield line

    def _next_side_effect():
        if handle.readline.return_value is not None:
            return handle.readline.return_value
        return next(_state[0])

    def _exit_side_effect(exctype, excinst, exctb):
        handle.close()

    global file_spec
    if file_spec is None:
        import _io
        file_spec = list(set(dir(_io.TextIOWrapper)).union(set(dir(_io.BytesIO))))

    global open_spec
    if open_spec is None:
        import _io
        open_spec = list(set(dir(_io.open)))
    if mock is None:
        mock = MagicMock(name='open', spec=open_spec)

    handle = MagicMock(spec=file_spec)