ncapply

#!/usr/bin/env python
# -*- coding: utf-8 -*-

from argparse import ArgumentParser
from netCDF4 import Dataset
import subprocess
import tempfile
import os


def main():
    '''
    Apply a netCDF CDL file to an existing dataset
    '''
    parser = ArgumentParser(description=main.__doc__)
    parser.add_argument('input')
    parser.add_argument('output')
    args = parser.parse_args()

    fd, path = tempfile.mkstemp()
    os.close(fd)

    subprocess.check_call(['ncgen', '-o', path, args.input])

    if os.path.exists(args.output):
        with Dataset(args.output, 'r') as nc_in:
            with Dataset(path, 'r+') as nc_out:
                for variable in nc_out.variables:
                    nc_out.variables[variable][:] = nc_in.variables[variable][:]

    os.rename(path, args.output)

if __name__ == '__main__':
    main()