Open an DataArray from a netCDF file containing a single data variable.

    This is designed to read netCDF files with only one data variable. If
    multiple variables are present then a ValueError is raised.

    Parameters
    ----------
    filename_or_obj : str, Path, file or xarray.backends.*DataStore
        Strings and Paths are interpreted as a path to a netCDF file or an
        OpenDAP URL and opened with python-netCDF4, unless the filename ends
        with .gz, in which case the file is gunzipped and opened with
        scipy.io.netcdf (only netCDF3 supported). Byte-strings or file-like
        objects are opened by scipy.io.netcdf (netCDF3) or h5py (netCDF4/HDF).
    group : str, optional
        Path to the netCDF4 group in the given file to open (only works for
        netCDF4 files).
    decode_cf : bool, optional
        Whether to decode these variables, assuming they were saved according
        to CF conventions.
    mask_and_scale : bool, optional
        If True, replace array values equal to `_FillValue` with NA and scale
        values according to the formula `original_values * scale_factor +
        add_offset`, where `_FillValue`, `scale_factor` and `add_offset` are
        taken from variable attributes (if they exist).  If the `_FillValue` or
        `missing_value` attribute contains multiple values a warning will be
        issued and all array values matching one of the multiple values will
        be replaced by NA. mask_and_scale defaults to True except for the
        pseudonetcdf backend.
    decode_times : bool, optional
        If True, decode times encoded in the standard NetCDF datetime format
        into datetime objects. Otherwise, leave them encoded as numbers.
    concat_characters : bool, optional
        If True, concatenate along the last dimension of character arrays to
        form string arrays. Dimensions will only be concatenated over (and
        removed) if they have no corresponding variable and if they are only
        used as the last dimension of character arrays.
    decode_coords : bool, optional
        If True, decode the 'coordinates' attribute to identify coordinates in
        the resulting dataset.
    engine : {'netcdf4', 'scipy', 'pydap', 'h5netcdf', 'pynio', 'cfgrib'}, \
        optional
        Engine to use when reading files. If not provided, the default engine
        is chosen based on available dependencies, with a preference for
        'netcdf4'.
    chunks : int or dict, optional
        If chunks is provided, it used to load the new dataset into dask
        arrays.
    lock : False or duck threading.Lock, optional
        Resource lock to use when reading data from disk. Only relevant when
        using dask or another form of parallelism. By default, appropriate
        locks are chosen to safely read and write files with the currently
        active dask scheduler.
    cache : bool, optional
        If True, cache data loaded from the underlying datastore in memory as
        NumPy arrays when accessed to avoid reading from the underlying data-
        store multiple times. Defaults to True unless you specify the `chunks`
        argument to use dask, in which case it defaults to False. Does not
        change the behavior of coordinates corresponding to dimensions, which
        always load their data from disk into a ``pandas.Index``.
    drop_variables: string or iterable, optional
        A variable or list of variables to exclude from being parsed from the
        dataset. This may be useful to drop variables with problems or
        inconsistent values.
    backend_kwargs: dictionary, optional
        A dictionary of keyword arguments to pass on to the backend. This
        may be useful when backend options would improve performance or
        allow user control of dataset processing.
    use_cftime: bool, optional
        Only relevant if encoded dates come from a standard calendar
        (e.g. 'gregorian', 'proleptic_gregorian', 'standard', or not
        specified).  If None (default), attempt to decode times to
        ``np.datetime64[ns]`` objects; if this is not possible, decode times to
        ``cftime.datetime`` objects. If True, always decode times to
        ``cftime.datetime`` objects, regardless of whether or not they can be
        represented using ``np.datetime64[ns]`` objects.  If False, always
        decode times to ``np.datetime64[ns]`` objects; if this is not possible
        raise an error.

    Notes
    -----
    This is designed to be fully compatible with `DataArray.to_netcdf`. Saving
    using `DataArray.to_netcdf` and then loading with this function will
    produce an identical result.

    All parameters are passed directly to `xarray.open_dataset`. See that
    documentation for further details.

    See also
    --------
    open_dataset

def open_dataarray(filename_or_obj, group=None, decode_cf=True,
                   mask_and_scale=None, decode_times=True, autoclose=None,
                   concat_characters=True, decode_coords=True, engine=None,
                   chunks=None, lock=None, cache=None, drop_variables=None,
                   backend_kwargs=None, use_cftime=None):
    """Open an DataArray from a netCDF file containing a single data variable.

    This is designed to read netCDF files with only one data variable. If
    multiple variables are present then a ValueError is raised.

    Parameters
    ----------
    filename_or_obj : str, Path, file or xarray.backends.*DataStore
        Strings and Paths are interpreted as a path to a netCDF file or an
        OpenDAP URL and opened with python-netCDF4, unless the filename ends
        with .gz, in which case the file is gunzipped and opened with
        scipy.io.netcdf (only netCDF3 supported). Byte-strings or file-like
        objects are opened by scipy.io.netcdf (netCDF3) or h5py (netCDF4/HDF).
    group : str, optional
        Path to the netCDF4 group in the given file to open (only works for
        netCDF4 files).
    decode_cf : bool, optional
        Whether to decode these variables, assuming they were saved according
        to CF conventions.
    mask_and_scale : bool, optional
        If True, replace array values equal to `_FillValue` with NA and scale
        values according to the formula `original_values * scale_factor +
        add_offset`, where `_FillValue`, `scale_factor` and `add_offset` are
        taken from variable attributes (if they exist).  If the `_FillValue` or
        `missing_value` attribute contains multiple values a warning will be
        issued and all array values matching one of the multiple values will
        be replaced by NA. mask_and_scale defaults to True except for the
        pseudonetcdf backend.
    decode_times : bool, optional
        If True, decode times encoded in the standard NetCDF datetime format
        into datetime objects. Otherwise, leave them encoded as numbers.
    concat_characters : bool, optional
        If True, concatenate along the last dimension of character arrays to
        form string arrays. Dimensions will only be concatenated over (and
        removed) if they have no corresponding variable and if they are only
        used as the last dimension of character arrays.
    decode_coords : bool, optional
        If True, decode the 'coordinates' attribute to identify coordinates in
        the resulting dataset.
    engine : {'netcdf4', 'scipy', 'pydap', 'h5netcdf', 'pynio', 'cfgrib'}, \
        optional
        Engine to use when reading files. If not provided, the default engine
        is chosen based on available dependencies, with a preference for
        'netcdf4'.
    chunks : int or dict, optional
        If chunks is provided, it used to load the new dataset into dask
        arrays.
    lock : False or duck threading.Lock, optional
        Resource lock to use when reading data from disk. Only relevant when
        using dask or another form of parallelism. By default, appropriate
        locks are chosen to safely read and write files with the currently
        active dask scheduler.
    cache : bool, optional
        If True, cache data loaded from the underlying datastore in memory as
        NumPy arrays when accessed to avoid reading from the underlying data-
        store multiple times. Defaults to True unless you specify the `chunks`
        argument to use dask, in which case it defaults to False. Does not
        change the behavior of coordinates corresponding to dimensions, which
        always load their data from disk into a ``pandas.Index``.
    drop_variables: string or iterable, optional
        A variable or list of variables to exclude from being parsed from the
        dataset. This may be useful to drop variables with problems or
        inconsistent values.
    backend_kwargs: dictionary, optional
        A dictionary of keyword arguments to pass on to the backend. This
        may be useful when backend options would improve performance or
        allow user control of dataset processing.
    use_cftime: bool, optional
        Only relevant if encoded dates come from a standard calendar
        (e.g. 'gregorian', 'proleptic_gregorian', 'standard', or not
        specified).  If None (default), attempt to decode times to
        ``np.datetime64[ns]`` objects; if this is not possible, decode times to
        ``cftime.datetime`` objects. If True, always decode times to
        ``cftime.datetime`` objects, regardless of whether or not they can be
        represented using ``np.datetime64[ns]`` objects.  If False, always
        decode times to ``np.datetime64[ns]`` objects; if this is not possible
        raise an error.

    Notes
    -----
    This is designed to be fully compatible with `DataArray.to_netcdf`. Saving
    using `DataArray.to_netcdf` and then loading with this function will
    produce an identical result.

    All parameters are passed directly to `xarray.open_dataset`. See that
    documentation for further details.

    See also
    --------
    open_dataset
    """

    dataset = open_dataset(filename_or_obj, group=group, decode_cf=decode_cf,
                           mask_and_scale=mask_and_scale,
                           decode_times=decode_times, autoclose=autoclose,
                           concat_characters=concat_characters,
                           decode_coords=decode_coords, engine=engine,
                           chunks=chunks, lock=lock, cache=cache,
                           drop_variables=drop_variables,
                           backend_kwargs=backend_kwargs,
                           use_cftime=use_cftime)

    if len(dataset.data_vars) != 1:
        raise ValueError('Given file dataset contains more than one data '
                         'variable. Please read with xarray.open_dataset and '
                         'then select the variable you want.')
    else:
        data_array, = dataset.data_vars.values()

    data_array._file_obj = dataset._file_obj

    # Reset names if they were changed during saving
    # to ensure that we can 'roundtrip' perfectly
    if DATAARRAY_NAME in dataset.attrs:
        data_array.name = dataset.attrs[DATAARRAY_NAME]
        del dataset.attrs[DATAARRAY_NAME]

    if data_array.name == DATAARRAY_VARIABLE:
        data_array.name = None

    return data_array