@jfpiolle Thank you very much for the clarification

@HasanAhmadQ7 You can have attributes of type list. See for instance this code:

``` from netCDF4 import Dataset import numpy

f = Dataset("example.nc","w") x = f.createDimension("x",3) vlvar = f.createVariable("test_var", numpy.int32, ("x"))

here create an attribute as a list

vlvar.test_attr = ["string a", "string b"]

vlvar[:] = numpy.arange(3) f.close() ```

Having files with different values for the test_attr attribute will cause open_mfdataset to fail.

thanks for addressing this!

@jfpiolle Would you please share the files, or the code generating them?

As far as I understand we cannot have an attribute of type list. The closest thing I can think of is a variable length type as below

from netCDF4 import Dataset f = Dataset("example.nc","w") vlen_t = f.createVLType(numpy.int32, "phony_vlen") x = f.createDimension("x",3) y = f.createDimension("y",4) vlvar = f.createVariable("phony_vlen_var", vlen_t, ("y","x")) data =[] for n in range(0, len(x)*len(y)): data.append(numpy.arange(random.randint(1,10),dtype="int32")) data = numpy.reshape(data,(len(y),len(x))) vlvar[:] = data f.close() Using files generated this way, I did not get an error using mf_dataset.

Thanks @HasanAhmadQ7, that would be fantastic !

I will handle this issue this Saturday if no one else handle it by then.

We could probably fix this by adding another case to equivalent for lists, e.g,. python elif isinstance(first, list) or isinstance(second, list): # verify both first and second are lists of the same length with the same elements # (by calling equivalent() on all elements)

Any interest in putting together a pull request for this? See http://xarray.pydata.org/en/stable/contributing.html