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pydap is an open-source implementation of the OPeNDAP protocol, written from scratch in pure Python. You can usepydap to access scientific data available on the many OPeNDAP servers publicly-available through the internet. Because pydap supports remote and lazy evaluation, you can access the data without having to download it; Instead, you work with special array and iterable objects that download data on-the-fly as necessary, saving bandwidth and time. The module also comes with a robust-but-lightweight OPeNDAP server, implemented as a WSGI application.

Originally developed in the 2000s,pydap is one of the oldest open-source Python projects available and is routinely developed and maintained by the OPeNDAP community at large. In addition,pydap is a long-recognized backend engine (and dependency) forxarray and chances are you have usedpydap in the past without knowing it.

pydap is a lightweight python package that you can use in either of the two modalities: a client and as a server. You can install the latest version usingpip. Afterinstalling pip you can installpydap with this command:

    $ pip install pydap

This will install pydap together with all the required dependencies.

pydap is also available throughAnaconda. Below we installpydap and its required dependencies, along with common additional packages in a fresh conda environment named"pydap":

    $ conda create -n pydap -c conda-forge python=3.11 pydap numpy jupyterlab ipython netCDF4 scipy matplotlib

Now you simply activate the pydap environment:

    $ conda activate pydap

You can now use pydap as a client and open any remotely served dataset, andpydap will download the accessed data on-the-fly as needed. For example considerthis dataset currently hosted on OPeNDAP's Hyrax data server

frompydap.clientimportopen_urlpyds=open_url('http://test.opendap.org:8080/opendap/catalog/ghrsst/20210102090000-JPL-L4_GHRSST-SSTfnd-MUR-GLOB-v02.0-fv04.1.nc',protocol='dap4')pyds.tree()

.20210102090000-JPL-L4_GHRSST-SSTfnd-MUR-GLOB-v02.0-fv04.1.nc    ├──time    ├──lat    ├──lon    ├──analysed_sst    ├──analysis_error    ├──mask    ├──sea_ice_fraction    ├──dt_1km_data    └──sst_anomaly

pyds['sst_anomaly'].shape

    (1,17999,36000)

pydap also comes with a simple server, implemented as aWSGI application. To use it, you first need to install the server and optionally a data handler:

    $ pip install"pydap[server,netcdf]"

This will install the necessary dependencies for running pydap as a server, along with extra dependencies for handlingnetCDF4 dataset. Now create a directory for your server data.

To run the server just issue the command:

    $ pydap --data ./myserver/data/ --port 8001 --workers 4 --threads 4

This will start a standalone server running on the defaulthttp://localhost:8001/, serving netCDF files from./myserver/data/ Since the server uses theWSGI standard, pydap uses by default one (1) worker and one (1) thread, but these can be defined by the user like in the case above (four (4) workers and four (4) threads).pydap can also easily be run behind Apache.

Theserver documentation has more information on how to better deploypydap.

For more information, seethe pydap documentation.

If you need any help withpydap, open an issue in this repository. You can also email themailing list. Finally, if you have a broader OPeNDAP access question, you can reach the OPeNDAP team on theOPeNDAP Discourse!