Logging and Exceptions

Exception Handling

pywgrib2_xr defines exception WgribError which is raised when a C function returns nonzero status. If that function writes an error message to stderr, it will be captured as exception value:

import pywgrib2_xr as pywgrib2

file = 'nonexistent'
try:
    pywgrib2.wgrib('nonexistent')
except WgribError as e:
    print(e)
finally:
    pywgrib2.free_files(file)

*** FATAL ERROR: missing input file nonexistent ***

*** arg list to wgrib2: wgrib2 nonexistent

The finally clause ensures that file is closed. The function wgrib does not close files on exit. One can try to set wgrib2 arguments '-transient', file, but this does not work when wgrib call fails:

file = 'gfs_tsoil.grib2'
try:
    pywgrib2.wgrib(file, '-foo', '-transient', file)
except Exception as e:
    print(e)
pywgrib2.status_open()

*** FATAL ERROR: unknown option -foo ***

*** arg list to wgrib2: wgrib2 gfs_tsoil.grib2 -foo -transient gfs_tsoil.grib2

<stdin>:1: UserWarning:
file: gfs_tsoil.grib2 r:perm file_offset=0 usage=0

The function status_open(), intended for debugging, prints files opened by the C code.

Logging

pywgrib2_xr uses Python module logging. By defaults, all emmited messages are output to Python’s stderr. It is possible to set logging level and a different output stream:

import logging
logging.basicConfig(filename='my.log', level=logging.DEBUG)
pywgrib2.wgrib('gfs.grib2', '-inv', 'gfs.inv')

cat my.log

DEBUG:pywgrib2_xr.wgrib2:args: ('gfs.grib2', '-inv', 'gfs.inv')

Setting level to DEBUG outputs arguments passed to wgrib.