Getting variable attributes from NetCDF MFDataset in Python

Question

I am loading multiple NetCDF files in python 3 (on Windows) using MFDataset, and am wanting to loop through the variables and look at the attributes. I am able to load and read the data fine, however I am wanting to access the attributes associated with the variables.

import netCDF4
file = r"C:\netcdf_files\data*.nc" #wildcarded NetCDF files

with netCDF4.MFDataset(file) as src:       
    for name, variable in src.variables.items():            
        for attrname in variable.ncattrs():
           print("{} -- {}".format(attrname, variable.getncattr(attrname)))

When the above snippet runs I am given a the following exception:

Traceback (most recent call last):
File "netCDF4\_netCDF4.pyx", line 5026, in netCDF4._netCDF4._Variable.__getattr__ (netCDF4\_netCDF4.c:57060)
KeyError: 'getncattr'

For a single file NetCDF file, loaded with Dataset:

import netCDF4
file = r"C:\netcdf_files\data1.nc" #single, explicit file

with netCDF4.Dataset(file) as src:       
    for name, variable in src.variables.items():            
        for attrname in variable.ncattrs():
           print("{} -- {}".format(attrname, variable.getncattr(attrname)))

The above runs just fine, printing out the variable attributes as desired.

I am still very new to working with NetCDF files - is there a way to access the variable attributes when loading data using MFDataset? Thanks!

Please provide the code which causes the error, preferably a minimal working (or in this case, not working) example. — Bart
– Bart, Commented Dec 17, 2015 at 10:06
Hi Bart, I have updated the post with some working examples - I hope they help to explain my issue. Cheers. — Steve
– Steve, Commented Dec 17, 2015 at 10:58

Bart · Accepted Answer · 2015-12-17 12:44:47Z

3

It seems that the getncattr function is indeed not available when using MFDataset. This solution seems to work with both Dataset and MFDataset:

import netCDF4

src = netCDF4.Dataset("drycblles.1.nc")

for name, variable in src.variables.items():            
    for attrname in variable.ncattrs():
        print("{} -- {}".format(attrname, getattr(variable, attrname)))
        # or :
        #print("{} -- {}".format(attrname, variable.getncattr(attrname))) 


src = netCDF4.MFDataset("drycblles.*.nc")

for name, variable in src.variables.items():            
    for attrname in variable.ncattrs():
        print("{} -- {}".format(attrname, getattr(variable, attrname)))

In both cases I get the same output.

edited Dec 17, 2015 at 12:44

answered Dec 17, 2015 at 12:38

Bart

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