Writing GRIB to a file target

# get input GRIB data
import earthkit.data as ekd

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

Using to_target() on the data object

We use to_target() to write the GRIB fieldlist/field into a file. The encoder is automatically guessed from the input data.

# writing a field
ds[0].to_target("file", "_res_t.grib")

# writing a whole fieldlist
ds.to_target("file", "_res_t.grib")

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

ekd.from_source("file", "_res_t.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	2t	2025-01-08 12:00:00	2025-01-08 12:00:00	0 days	0	surface	0	regular_ll	8
1	msl	2025-01-08 12:00:00	2025-01-08 12:00:00	0 days	0	surface	0	regular_ll	8

# data can be appended to the output file
ds[1].to_target("file", "_res_t.grib")
ds[0].to_target("file", "_res_t.grib", append=True)
ekd.from_source("file", "_res_t.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	msl	2020-05-13 12:00:00	2020-05-13 12:00:00	0 days	0	surface	0	regular_ll	16
1	2t	2020-05-13 12:00:00	2020-05-13 12:00:00	0 days	0	surface	0	regular_ll	16

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", "_res_t.grib")
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", "_res_t.grib") as target:
    target.write(ds)

# a filedlist can be written field by field into the target
with ekd.create_target("file", "_res_t.grib") 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", "_res_t.grib", metadata={"date": 20250108}, bitsPerValue=8)

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

# using an encoder object
encoder = ekd.create_encoder("grib", metadata={"date": 20250108})
ds.to_target("file", "_res_t.grib", 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", "_res_t.grib") as target:
    target.write(ds, encoder=encoder, bitsPerValue=8)