LazyPolarsDataset

LazyPolarsDataset loads and saves data using Polars in lazy execution mode.

kedro_datasets.polars.LazyPolarsDataset

LazyPolarsDataset(
    *,
    filepath,
    file_format,
    load_args=None,
    save_args=None,
    version=None,
    credentials=None,
    fs_args=None,
    metadata=None
)

Bases: AbstractVersionedDataset[LazyFrame, LazyFrame | DataFrame]

LazyPolarsDataset loads/saves data from/to a data file using an underlying filesystem (e.g.: local, S3, GCS). It uses Polars to handle the type of read/write target. It uses lazy loading with Polars Lazy API, but it can save both Lazy and Eager Polars DataFrames.

Examples:

Using the YAML API:

cars:
  type: polars.LazyPolarsDataset
  filepath: data/01_raw/company/cars.csv
  load_args:
    sep: ","
    parse_dates: False
  save_args:
    has_header: False
    null_value: "somenullstring"

motorbikes:
  type: polars.LazyPolarsDataset
  filepath: s3://your_bucket/data/02_intermediate/company/motorbikes.csv
  credentials: dev_s3

Using the Python API:

>>> import polars as pl
>>> from kedro_datasets.polars import LazyPolarsDataset
>>>
>>> data = pl.DataFrame({"col1": [1, 2], "col2": [4, 5], "col3": [5, 6]})
>>>
>>> dataset = LazyPolarsDataset(filepath=tmp_path / "test.csv", file_format="csv")
>>> dataset.save(data)
>>> reloaded = dataset.load()
>>> assert data.equals(reloaded.collect())

Parameters:

• filepath (str) –

  Filepath in POSIX format to a file prefixed with a protocol like s3://. If prefix is not provided, file protocol (local filesystem) will be used. The prefix should be any protocol supported by fsspec. Key assumption: The first argument of either load/save method points to a filepath/buffer/io type location. There are some read/write targets such as 'clipboard' or 'records' that will fail since they do not take a filepath like argument.

• file_format (str) –

  String which is used to match the appropriate load/save method on a best effort basis. For example if 'csv' is passed the polars.read_csv and polars.DataFrame.write_csv methods will be identified. An error will be raised unless at least one matching read_{file_format} or write_{file_format}.

• load_args (dict[str, Any] | None, default: None ) –

  polars options for loading files. Here you can find all available arguments: https://pola-rs.github.io/polars/py-polars/html/reference/io.html All defaults are preserved.

• save_args (dict[str, Any] | None, default: None ) –

  Polars options for saving files. Here you can find all available arguments: https://pola-rs.github.io/polars/py-polars/html/reference/io.html All defaults are preserved.

• version (Version | None, default: None ) –

  If specified, should be an instance of kedro.io.core.Version. If its load attribute is None, the latest version will be loaded. If its save attribute is None, save version will be autogenerated.

• credentials (dict[str, Any] | None, default: None ) –

  Credentials required to get access to the underlying filesystem. E.g. for GCSFileSystem it should look like {"token": None}.

• fs_args (dict[str, Any] | None, default: None ) –

  Extra arguments to pass into underlying filesystem class constructor (e.g. {"project": "my-project"} for GCSFileSystem), as well as to pass to the filesystem's open method through nested keys open_args_load and open_args_save. Here you can find all available arguments for open: https://filesystem-spec.readthedocs.io/en/latest/api.html#fsspec.spec.AbstractFileSystem.open All defaults are preserved, except mode, which is set to wb when saving.

• metadata (dict[str, Any] | None, default: None ) –

  Any arbitrary metadata. This is ignored by Kedro, but may be consumed by users or external plugins.

Raises: DatasetError: Will be raised if at least less than one appropriate read or write methods are identified.

Source code in kedro_datasets/polars/lazy_polars_dataset.py

def __init__(  # noqa: PLR0913
    self,
    *,
    filepath: str,
    file_format: str,
    load_args: dict[str, Any] | None = None,
    save_args: dict[str, Any] | None = None,
    version: Version | None = None,
    credentials: dict[str, Any] | None = None,
    fs_args: dict[str, Any] | None = None,
    metadata: dict[str, Any] | None = None,
) -> None:
    """Creates a new instance of ``LazyPolarsDataset`` pointing to a concrete
    data file on a specific filesystem.

    Args:
        filepath: Filepath in POSIX format to a file prefixed with a protocol like
            `s3://`.
            If prefix is not provided, `file` protocol (local filesystem)
            will be used.
            The prefix should be any protocol supported by ``fsspec``.
            Key assumption: The first argument of either load/save method points to
            a filepath/buffer/io type location. There are some read/write targets
            such as 'clipboard' or 'records' that will fail since they do not take a
            filepath like argument.
        file_format: String which is used to match the appropriate load/save method
            on a best effort basis. For example if 'csv' is passed the
            `polars.read_csv` and
            `polars.DataFrame.write_csv` methods will be identified. An error will
            be raised unless
            at least one matching `read_{file_format}` or `write_{file_format}`.
        load_args: polars options for loading files.
            Here you can find all available arguments:
            https://pola-rs.github.io/polars/py-polars/html/reference/io.html
            All defaults are preserved.
        save_args: Polars options for saving files.
            Here you can find all available arguments:
            https://pola-rs.github.io/polars/py-polars/html/reference/io.html
            All defaults are preserved.
        version: If specified, should be an instance of
            ``kedro.io.core.Version``. If its ``load`` attribute is
            None, the latest version will be loaded. If its ``save``
            attribute is None, save version will be autogenerated.
        credentials: Credentials required to get access to the underlying filesystem.
            E.g. for ``GCSFileSystem`` it should look like `{"token": None}`.
        fs_args: Extra arguments to pass into underlying filesystem class constructor
            (e.g. `{"project": "my-project"}` for ``GCSFileSystem``), as well as
            to pass to the filesystem's `open` method through nested keys
            `open_args_load` and `open_args_save`.
            Here you can find all available arguments for `open`:
            https://filesystem-spec.readthedocs.io/en/latest/api.html#fsspec.spec.AbstractFileSystem.open
            All defaults are preserved, except `mode`, which is set to `wb` when saving.
        metadata: Any arbitrary metadata.
            This is ignored by Kedro, but may be consumed by users or external plugins.
    Raises:
        DatasetError: Will be raised if at least less than one appropriate
            read or write methods are identified.
    """
    self._file_format = file_format.lower()

    if self._file_format not in ACCEPTED_FILE_FORMATS:
        raise DatasetError(
            f"'{self._file_format}' is not an accepted format "
            f"({ACCEPTED_FILE_FORMATS}) ensure that your 'file_format' parameter "
            "has been defined correctly as per the Polars API "
            "https://pola-rs.github.io/polars/py-polars/html/reference/io.html"
        )

    _fs_args = deepcopy(fs_args) or {}
    _fs_open_args_load = _fs_args.pop("open_args_load", {})
    _fs_open_args_save = _fs_args.pop("open_args_save", {})
    _credentials = deepcopy(credentials) or {}

    protocol, path = get_protocol_and_path(filepath, version)
    if protocol == "file":
        _fs_args.setdefault("auto_mkdir", True)

    self._protocol = protocol
    self._storage_options = {**_credentials, **_fs_args}
    self._fs = fsspec.filesystem(self._protocol, **self._storage_options)

    self.metadata = metadata

    super().__init__(
        filepath=PurePosixPath(path),
        version=version,
        exists_function=self._fs.exists,
        glob_function=self._fs.glob,
    )

    # Handle default load and save and fs arguments
    self._load_args = {**self.DEFAULT_LOAD_ARGS, **(load_args or {})}
    self._save_args = {**self.DEFAULT_SAVE_ARGS, **(save_args or {})}
    self._fs_open_args_load = {
        **self.DEFAULT_FS_ARGS.get("open_args_load", {}),
        **(_fs_open_args_load or {}),
    }
    self._fs_open_args_save = {
        **self.DEFAULT_FS_ARGS.get("open_args_save", {}),
        **(_fs_open_args_save or {}),
    }

    if "storage_options" in self._save_args or "storage_options" in self._load_args:
        logger.warning(
            "Dropping 'storage_options' for %s, "
            "please specify them under 'fs_args' or 'credentials'.",
            self._filepath,
        )
        self._save_args.pop("storage_options", None)
        self._load_args.pop("storage_options", None)

DEFAULT_FS_ARGS class-attribute instance-attribute

DEFAULT_FS_ARGS = {'open_args_save': {'mode': 'wb'}}

DEFAULT_LOAD_ARGS class-attribute

DEFAULT_LOAD_ARGS = {}

DEFAULT_SAVE_ARGS class-attribute

DEFAULT_SAVE_ARGS = {}

_file_format instance-attribute

_file_format = lower()

_fs instance-attribute

_fs = filesystem(_protocol, **(_storage_options))

_fs_open_args_load instance-attribute

_fs_open_args_load = {
    None: get("open_args_load", {}),
    None: _fs_open_args_load or {},
}

_fs_open_args_save instance-attribute

_fs_open_args_save = {
    None: get("open_args_save", {}),
    None: _fs_open_args_save or {},
}

_load_args instance-attribute

_load_args = {
    None: DEFAULT_LOAD_ARGS,
    None: load_args or {},
}

_protocol instance-attribute

_protocol = protocol

_save_args instance-attribute

_save_args = {
    None: DEFAULT_SAVE_ARGS,
    None: save_args or {},
}

_storage_options instance-attribute

_storage_options = {None: _credentials, None: _fs_args}

metadata instance-attribute

metadata = metadata

_describe

_describe()

Source code in kedro_datasets/polars/lazy_polars_dataset.py

def _describe(self) -> dict[str, Any]:
    return {
        "filepath": self._filepath,
        "protocol": self._protocol,
        "load_args": self._load_args,
        "save_args": self._save_args,
        "version": self._version,
    }

_exists

_exists()

Source code in kedro_datasets/polars/lazy_polars_dataset.py

def _exists(self) -> bool:
    try:
        load_path = get_filepath_str(self._get_load_path(), self._protocol)
    except DatasetError:  # pragma: no cover
        return False

    return self._fs.exists(load_path)

_invalidate_cache

_invalidate_cache()

Invalidate underlying filesystem caches.

Source code in kedro_datasets/polars/lazy_polars_dataset.py

def _invalidate_cache(self) -> None:
    """Invalidate underlying filesystem caches."""
    filepath = get_filepath_str(self._filepath, self._protocol)
    self._fs.invalidate_cache(filepath)

_release

_release()

Source code in kedro_datasets/polars/lazy_polars_dataset.py

def _release(self) -> None:
    super()._release()
    self._invalidate_cache()

load

load()

Source code in kedro_datasets/polars/lazy_polars_dataset.py

def load(self) -> pl.LazyFrame:
    load_path = str(self._get_load_path())
    if not self._exists():
        raise FileNotFoundError(errno.ENOENT, os.strerror(errno.ENOENT), load_path)

    if self._protocol == "file":
        # With local filesystems, we can use Polar's build-in I/O method:
        self._load_args.pop("partitioning", None)
        load_method = getattr(pl, f"scan_{self._file_format}", None)
        return load_method(load_path, **self._load_args)  # type: ignore[misc]

    # For object storage, we use pyarrow for I/O:
    dataset = ds.dataset(
        load_path, filesystem=self._fs, format=self._file_format, **self._load_args
    )
    return pl.scan_pyarrow_dataset(dataset)

save

save(data)

Source code in kedro_datasets/polars/lazy_polars_dataset.py

def save(self, data: pl.DataFrame | pl.LazyFrame) -> None:
    save_path = get_filepath_str(self._get_save_path(), self._protocol)

    collected_data = None
    if isinstance(data, pl.LazyFrame):
        collected_data = data.collect()
    else:
        collected_data = data

    # Note: polars does support writing partitioned parquet file
    # it is leveraging Arrow to do so, see e.g.
    # https://pola-rs.github.io/polars/py-polars/html/reference/api/polars.DataFrame.write_parquet.html
    save_method = getattr(collected_data, f"write_{self._file_format}", None)
    if save_method:
        if self._save_args.get("use_pyarrow") is True:
            pyarrow_opts = self._save_args.get("pyarrow_options", {})
            pa_fs = PyFileSystem(FSSpecHandler(self._fs))
            pyarrow_opts["filesystem"] = pa_fs
            self._save_args["pyarrow_options"] = pyarrow_opts
            save_method(file=save_path, **self._save_args)
        else:
            with self._fs.open(save_path, **self._fs_open_args_save) as fs_file:
                save_method(file=fs_file, **self._save_args)
            self._invalidate_cache()
    # How the LazyPolarsDataset logic is currently written with
    # ACCEPTED_FILE_FORMATS and a check in the `__init__` method,
    # this else loop is never reached, hence we exclude it from coverage report
    # but leave it in for consistency between the Eager and Lazy classes
    else:  # pragma: no cover
        raise DatasetError(
            f"Unable to retrieve 'polars.DataFrame.write_{self._file_format}' "
            "method, please ensure that your 'file_format' parameter has been "
            "defined correctly as per the Polars API"
            "https://pola-rs.github.io/polars/py-polars/html/reference/dataframe/index.html"
        )