open or create a netcdf file given by filename. This function returns a netcdf file object. Possible values of mode are:
- "r", "nowrite": opens an existing file in read-only mode.
- "w", "write": opens an existing file in read-write mode.
- "c", "clobber": creates a new file and possibly overwrites existing data sets.
- "nc", "noclobber": creates a new file but an existing data sets in the netcdf file cannot be overwritten.
When a new file is created, the format can be specified:
- "classic": The default format subjected to the limitation described in http://www.unidata.ucar.edu/software/netcdf/docs/netcdf/NetCDF-Classic-Format-Limitations.html
- "64bit-offset": For large file and data sets. This format was introduced in NetCDF 3.6.0.