problem with netCDF4 OpenDAP

Fri Aug 14 09:15:17 EDT 2015

> On Aug 14, 2015, at 3:18 AM, Tom P <werotizy at freent.dd> wrote:
> 
> Thanks for the reply but that is not what the documentation says.
> 
> http://unidata.github.io/netcdf4-python/#section8
> "Remote OPeNDAP-hosted datasets can be accessed for reading over http if a URL is provided to the netCDF4.Dataset constructor instead of a filename. However, this requires that the netCDF library be built with OPenDAP support, via the --enable-dap configure option (added in version 4.0.1).”

Huh, so it does.  Your error message says "file not found", though, which suggested to me that it's trying to interpret the NetCDF file as a local file instead of a URL.  Indeed, when I run that example, the traceback is more complete (the traceback you printed had omitted some information):

>>> netCDF4.Dataset('http://www1.ncdc.noaa.gov/pub/data/cmb/ersst/v3b/netcdf/ersst.201507.nc')
syntax error, unexpected WORD_WORD, expecting SCAN_ATTR or SCAN_DATASET or SCAN_ERROR
context: <!DOCTYPE^ HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"><html><head><title>404 Not Found</title></head><body><h1>Not Found</h1><p>The requested URL /pub/data/cmb/ersst/v3b/netcdf/ersst.201507.nc.dds was not found on this server.</p></body></html>
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "netCDF4/_netCDF4.pyx", line 1547, in netCDF4._netCDF4.Dataset.__init__ (netCDF4/_netCDF4.c:9551)
RuntimeError: NetCDF: file not found

So it’s clear that netCDF4 is at least *trying* to go online to look for the file, but it simply can’t find it.  Since the docs say it’s linking to libcurl, I tried using curl to download the file (curl -# http://www1.ncdc.noaa.gov/pub/data/cmb/ersst/v3b/netcdf/ersst.201507.nc > test.nc) and it worked fine.  What’s more, it *seems* like the file (/pub/.../ersst.201507.nc.dds) was decorated with the ‘.dds’ suffix for some reason (not sure if the server redirected the request there or not).  But this looks like a netCDF4 issue.  Perhaps you can go to their project page on Github and file an issue there -- they will be more likely to have your answer than people here.

HTH,
Jason

> 
> and for the Anaconda package -
> http://docs.continuum.io/anaconda/changelog
> "2013-05-08: 1.5.0:
> Highlights:
>  updates to all important packages: python, numpy, scipy, ipython, matplotlib, pandas, cython
>  added netCDF4 (with OpenDAP support) on Linux and MacOSX"
> 
> -- 
> https://mail.python.org/mailman/listinfo/python-list

--
Jason M. Swails
BioMaPS,
Rutgers University
Postdoctoral Researcher