Writing GRIB to file-pattern target

# get input GRIB data
import earthkit.data as ekd

ds = ekd.from_source("sample", "tuv_pl.grib").to_fieldlist()

Using to_target() on the data object

We use to_target() to write the GRIB fieldlist/field with a :ref:`targets-file-pattern`to disc. The encoder is automatically guessed from the input data. We use the following output file name pattern:

# for each shortName-level combination a separate output file will be created
out_pattern = "_res_pattern_{metadata.shortName}_{metadata.level}.grib"

# writing only temperature fields
ds.sel({"parameter.variable": "t"}).to_target("file-pattern", out_pattern)

# writing a whole fieldlist
ds.to_target("file-pattern", out_pattern)

# checking one output file
ekd.from_source("file", "_res_pattern_t_850.grib").to_fieldlist().ls()

	parameter.variable	time.valid_datetime	time.base_datetime	time.step	vertical.level	vertical.level_type	ensemble.member	geography.grid_type
0	t	2018-08-01 12:00:00	2018-08-01 12:00:00	0 days	850	pressure	0	regular_ll

# setting GRIB keys for the output
ds.to_target("file-pattern", out_pattern, metadata={"date": 20250108}, bitsPerValue=8)

# checking one output file
ekd.from_source("file", "_res_pattern_t_850.grib").to_fieldlist().ls(extra_keys=["metadata.bitsPerValue"])

	parameter.variable	time.valid_datetime	time.base_datetime	time.step	vertical.level	vertical.level_type	ensemble.member	geography.grid_type	metadata.bitsPerValue
0	t	2025-01-08 12:00:00	2025-01-08 12:00:00	0 days	850	pressure	0	regular_ll	8

Using a Target object

We can create a target object with get_target() and use write() to write/add data to it.

# basic usage
target = ekd.create_target("file-pattern", out_pattern)
target.write(ds)
target.close()

# can be used as a context manager, no need to call close() in the end
with ekd.create_target("file-pattern", out_pattern) as target:
    target.write(ds)

# a fieldlist can be written field by field into the target
with ekd.create_target("file-pattern", out_pattern) as target:
    for f in ds:
        target.write(f)

Using encoders

These calls are equivalent.

# setting metadata and other GRIB keys for the output
ds.to_target("file-pattern", out_pattern, metadata={"date": 20250108}, bitsPerValue=8)

# explicitly specifying the encoder
ds.to_target("file-pattern", out_pattern, encoder="grib", metadata={"date": 20250108}, bitsPerValue=8)

# using an encoder object
encoder = ekd.create_encoder("grib", metadata={"date": 20250108})
ds.to_target("file-pattern", out_pattern, encoder=encoder, bitsPerValue=8)

The same can be done with a target object.

encoder = ekd.create_encoder("grib", metadata={"date": 20250108})
with ekd.create_target("file-pattern", out_pattern) as target:
    target.write(ds, encoder=encoder, bitsPerValue=8)