#!/usr/bin/env python3

# this version does a call to wgrib2 to netcdf files
# does not make or use inventory file

import pywgrib2_s
in_file='gfs.t00z.master.grb2f048'
outa='gfs_1a.nc'
outb='gfs_1b.nc'

err = pywgrib2_s.wgrib2( [in_file, '-rewind_init', in_file, '-match',':HGT:500 mb:', "-netcdf", outa] )
print("write netcdf-a=",err)
err = pywgrib2_s.wgrib2( [in_file, '-rewind_init', in_file, '-match',':TMP:850 mb:', "-netcdf", outb] )
print("write netcdf-b=",err)

Usage

ierr = pywgrib2_s.wgrib2( [ (list of wgrib2 arguments) ] )
      note: output files remain open and may not be flushed
            previously opened output files will continue writing after last write
            input files remain open
            previously opened input files will continue reading after last read

      note: you can flush the output file by closing the file by pywgrib2_s.close(file)
      note: you can read from the beginning of a file by '-rewind_init', file after the
            file has been opened

Version and Configuration of Wgrib2 Routine

result = pywgrib2_s.wgrib2_version()
         result is a string with the wgrib2 version (same as wgrib2 -version)

result = pywgrib2_s.wgrib2_configuration()
         result is a list of strings
         the same as wgrib2 -config

How it works

John Howard (2014) submitted changes that optionally make wgrib2 a routine rather than a program. The arguments to the wgrib2 routine were the same as the arguments to the wgrib2 the program. Since wgrib2 is written in C, the arguments to wgrib2 are the length of the array of strings followed by an array of pointers to strings. Being a C program, the strings are terminated by a zero.

The pywgrib2_s loads a shared wgrib2 library and calls the "wgrib2" using the following python code.

def wgrib2(arg):
    #
    #    call wgrib2
    #        ex.  pywgrib2.wgrib2(["in.grb","-inv","@mem.0"])
    #
    #    uses C calling convention: 1st arg is name of program
    #
    global debug
    arg_length = len(arg) + 1
    select_type = (c_char_p * arg_length)
    select = select_type()
    item = "pywgrib2"
    select[0] = item.encode('utf-8')

    for key, item in enumerate(arg):
        select[key + 1] = item.encode('utf-8')

    if debug: print("wgrib2 args: ", arg)
    ierr = my_wgrib2.wgrib2(arg_length, select)
    if debug: print("wgrib2 err=", ierr)
    return ierr

See also: