Function _extract_nc4_variable_encoding

xarray/backends/netCDF4_.py:255–329

(
    variable: Variable,
    raise_on_invalid=False,
    lsd_okay=True,
    h5py_okay=False,
    backend="netCDF4",
    unlimited_dims=None,
)

def _extract_nc4_variable_encoding(
    variable: Variable,
    raise_on_invalid=False,
    lsd_okay=True,
    h5py_okay=False,
    backend="netCDF4",
    unlimited_dims=None,
) -> dict[str, Any]:
    if unlimited_dims is None:
        unlimited_dims = ()

    encoding = variable.encoding.copy()

    safe_to_drop = {"source", "original_shape"}
    valid_encodings = {
        "zlib",
        "complevel",
        "fletcher32",
        "contiguous",
        "chunksizes",
        "shuffle",
        "_FillValue",
        "dtype",
        "compression",
        "significant_digits",
        "quantize_mode",
        "blosc_shuffle",
        "szip_coding",
        "szip_pixels_per_block",
        "endian",
    }
    if lsd_okay:
        valid_encodings.add("least_significant_digit")
    if h5py_okay:
        valid_encodings.add("compression_opts")

    if not raise_on_invalid and encoding.get("chunksizes") is not None:
        # It's possible to get encoded chunksizes larger than a dimension size
        # if the original file had an unlimited dimension. This is problematic
        # if the new file no longer has an unlimited dimension.
        chunksizes = encoding["chunksizes"]
        chunks_too_big = any(
            c > d and dim not in unlimited_dims
            for c, d, dim in zip(
                chunksizes, variable.shape, variable.dims, strict=False
            )
        )
        has_original_shape = "original_shape" in encoding
        changed_shape = (
            has_original_shape and encoding.get("original_shape") != variable.shape
        )
        if chunks_too_big or changed_shape:
            del encoding["chunksizes"]

    var_has_unlim_dim = any(dim in unlimited_dims for dim in variable.dims)
    if not raise_on_invalid and var_has_unlim_dim and "contiguous" in encoding.keys():
        del encoding["contiguous"]