Hi,
When we recently relinked our software products, NCL and PyNIO, with
the newly released version of
the NetCDF 4.0 library we discovered that there seems to have been a
change in the actual, as opposed
to the documented, rules for variable names. Specifically it appears
that names that begin with a digit can no longer
be written to NetCDF files. This change causes difficulties for our
software, particularly with our
conversion utility, ncl_convert2nc, when used to convert GRIB to
NetCDF. Our GRIB reader uses GRIB
parameter names, as published by NCEP and other sources such as
ECMWF, as the initial characters of GRIB
variable names. A number of these parameter names (e.g. "4LFTX",
"5WAVH", and "5WAVA" from NCEP's
operational table) begin with digits. Now suddenly with the new
version of NetCDF file conversions
that have worked for many years no longer complete successfully.
Since first encountering this problem, I have discovered 2 additional
points: (1) the new NetCDF 3.6.3 library
has the same behavior as the 4.0 library and (2) neither version of
the library (fortunately) has a problem reading existing
files that contain variable names that begin with digits.
Admittedly, NCL and our file I/O library should have been coded to
follow the documented behavior rather than
the actual behavior of the NetCDF library. However, initial digits in
variable names have worked for at least the last 10 years,
and were working as recently as netcdf-4.0-beta1. Assuming the change
was intentional, I wonder if the developers realized
the serious backwards incompatibility that could result for client
software. It seems to me that a user-visible change like this
should have been announced for at least a few months. It should not
have taken place without warning between a beta
and a final release. However, perhaps the change was inadvertent. In
any case is there a possibility of treating this as a bug
and reverting to the older behavior at least for awhile? Actually I
wonder what the need is to restrict names in this fashion
other than just to satisfy the written documentation. Why not allow
initial digits in names when they have worked just fine for many years?
-Dave Brown
NCL, PyNGL/PyNIO development team
