Writing to a NetCDF3 file using module netcdf4 in python - python-3.x

Question

I'm having a issue writing to a netcdf3 file using the netcdf4 functions. I tried using the create variable function but it gives me this error: NetCDF: Attempting netcdf-4 operation on netcdf-3 file
nc = Dataset(root.fileName,'a',format="NETCDF4")
Hycom_U = nc.createVariable('/variables/Hycom_U','float',('time','lat','lon',))
Hycom_V = nc.createVariable('/variables/Hycom_V','f4',('time','lat','lon',))
nc=
root group (NETCDF3_CLASSIC data model, file format NETCDF3):
netcdf_library_version: 4.1.3
format_version: HFRNet_1.0.0
product_version: HFRNet_1.1.05
Conventions: CF-1.0
title: Near-Real Time Surface Ocean Velocity, Hawaii,
2 km Resolution
institution: Scripps Institution of Oceanography
source: Surface Ocean HF-Radar
history: 22-Feb-2017 00:55:46: NetCDF file created
22-Feb-2017 00:55:46: Filtered U and V by GDOP < 1.25 ;
FMRC Best Dataset
references: Terrill, E. et al., 2006. Data Management and Real-time
Distribution in the HF-Radar National Network. Proceedings
of the MTS/IEEE Oceans 2006 Conference, Boston MA,
September 2006.
creator_name: Mark Otero
creator_email: motero#ucsd.edu
creator_url: http://cordc.ucsd.edu/projects/mapping/
summary: Surface ocean velocities estimated from HF-Radar are
representative of the upper 0.3 - 2.5 meters of the
ocean. The main objective of near-real time
processing is to produce the best product from
available data at the time of processing. Radial
velocity measurements are obtained from individual
radar sites through the U.S. HF-Radar Network.
Hourly radial data are processed by unweighted
least-squares on a 2 km resolution grid of Hawaii
to produce near real-time surface current maps.
geospatial_lat_min: 20.487279892
geospatial_lat_max: 21.5720806122
geospatial_lon_min: -158.903594971
geospatial_lon_max: -157.490005493
grid_resolution: 2km
grid_projection: equidistant cylindrical
regional_description: Unites States, Hawaiian Islands
cdm_data_type: GRID
featureType: GRID
location: Proto fmrc:HFRADAR,_US_Hawaii,_2km_Resolution,_Hourly_RTV
History: Translated to CF-1.0 Conventions by Netcdf-Java CDM (NetcdfCFWriter)
Original Dataset = fmrc:HFRADAR,_US_Hawaii,_2km_Resolution,_Hourly_RTV; Translation Date = Thu Feb 23 13:35:32 GMT 2017
dimensions(sizes): time(25), lat(61), lon(77)
variables(dimensions): float32 u(time,lat,lon), float64 time_run(time), float64 time(time), float32 lat(lat), float32 lon(lon), float32 v(time,lat,lon)
groups:
What are the netcdf 3 operations I can use to add data into the file? I found out that I could manually add data by simply doing this nc.variables["Hycom_U"]=U2which directly adds the data, but nothing else. Is there a better way to do this?

Answer 1

I believe the issue is that you're claiming the file to be netCDF4 format:
nc = Dataset(root.fileName,'a',format="NETCDF4")`
but you really want to indicate that it's netCDF3:
nc = Dataset(root.fileName,'a',format="NETCDF3_CLASSIC")
Additional documentation can be found here.

Answer 2

I figured it out! I simply couldn't use a path as a varname.
Hycom_U = nc.createVariable('Hycom_U','float',('time','lat','lon',))
It properly created a variable for me.