eccodes/examples/python/grib_samples.py

#
# (C) Copyright 2005- ECMWF.
#
# This software is licensed under the terms of the Apache Licence Version 2.0
# which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
#
# In applying this licence, ECMWF does not waive the privileges and immunities
# granted to it by virtue of its status as an intergovernmental organisation
# nor does it submit to any jurisdiction.
#

import sys
import traceback

from eccodes import *

INPUT = "../../data/tp_ecmwf.grib"
OUTPUT = "p_out.grib_samples.grib"
VERBOSE = 1  # verbose error reporting


def example():
    sample_id = codes_grib_new_from_samples("regular_ll_sfc_grib1")
    fin = open(INPUT, "rb")
    fout = open(OUTPUT, "wb")

    keys = {
        "dataDate": 20080104,
        "startStep": 0,
        "endStep": 12,
        "stepType": "accum",
        "table2Version": 2,
        "indicatorOfParameter": 61,
        "decimalPrecision": 2,
    }

    prev_vals = None
    while 1:
        gid = codes_grib_new_from_file(fin)
        if gid is None:
            break

        curr_vals = codes_get_values(gid)

        if prev_vals is None:
            result = prev_vals = curr_vals
        else:
            try:
                # works with NumPy
                result = curr_vals - prev_vals
            except TypeError:  # but not with array
                result = curr_vals
                for i in range(len(result)):
                    result[i] -= prev_vals[i]

            prev_vals = curr_vals
            keys["startStep"] += 12
            keys["endStep"] += 12

        clone_id = codes_clone(sample_id)

        for key in keys:
            codes_set(clone_id, key, keys[key])

        codes_set_values(clone_id, result * 1000)

        codes_write(clone_id, fout)

        codes_release(gid)

    fin.close()
    fout.close()


def main():
    try:
        example()
    except CodesInternalError as err:
        if VERBOSE:
            traceback.print_exc(file=sys.stderr)
        else:
            sys.stderr.write(err.msg + "\n")

        return 1


if __name__ == "__main__":
    sys.exit(main())