check_child_attr_data_types error from cf tests

[ancillary]

We are getting the following error message from the cf:1.7 and cf:1.6 tests run on this netcdf file (and all of our other netcdf files).

Running Compliance Checker on the datasets from: ['A0101.ocean.001m.merged.nc']
WARNING: The following exceptions occured during the cf:1.7 checker (possibly indicate compliance checker issues):
cf:1.7.check_child_attr_data_types: 'bytes' object has no attribute 'dtype'
File "c:\apps\anaconda3\envs\ioosalt\lib\site-packages\compliance_checker\cf\cf.py", line 1245, in check_child_attr_data_types
self._parent_var_attr_type_check(att_name, var, ctx)
File "c:\apps\anaconda3\envs\ioosalt\lib\site-packages\compliance_checker\cf\cf.py", line 442, in _parent_var_attr_type_check
val_type = attr_val.dtype.type

Currently using 4.3.3rc2, but we have seen the same message with 4.3.3rc1, and 4.3.2.

Is there some issue with the dataset I am missing? Although this example uses scale_factor = 1. and add_offest = 0. attributes, we get the same error if these attributes are omitted.

[benjwadams]

Curious. For some reason the string-like value _FillValue is getting side as bytes here. In pretty much all string-like attributes, str is returned under Python 3.

In the offending variable, missing_value is also "0", but is a str type when read through netCDF4-Python:

ipdb> var
<class 'netCDF4._netCDF4.Variable'>
|S1 conductivity_qc_tests(time, number_tests)
    long_name: conductivity QARTOD Individual Tests
    standard_name: conductivity status_flag
    short_name: CONDQTST
    intent: data_quality
    _FillValue: b'0'
    missing_value: 0
    flag_values: 1 2 3 4 9
    flag_meanings: PASS NOT_EVALUATED SUSPECT FAIL MISSING
    comments: 14-character array with results of individual QARTOD tests.  1:Gap, 2:Syntax, 3:Location, 4:Gross Range, 5:Climatology, 6:Spike, 7:Rate of Change, 8:Flat-line, 9:Multi-variate,
 10:Attenuated Signal, 11:Neighbor, 12:Associated variable, 13:Manual, 14:Other
unlimited dimensions: time
current shape = (5641, 14)
filling on
ipdb> var.flag_values
'1 2 3 4 9'
ipdb> var.missing_value
'0'
ipdb> type(var.missing_value)
<class 'str'>
ipdb> type(var._FillValue)
<class 'bytes'>

[benjwadams]

Since merging #783, unhandled exceptions no longer occur when a bytes value is input to _FillValue, among others. Closing.