The following packages are required to work with ESMPy:

The following packages are optional:

  • ESMF installation with NetCDF - required to create Grids and Meshes from file
    • NetCDF must be built as a shared library for ESMPy installation to succeed
  • mpi4py- python bindings to MPI, needed to run some of the parallel regridding examples

  • nose - for nose testing

Getting the code

The ESMF User’s Guide contains information on building and installing ESMF. The ESMF Reference Manual contains information on the architecture of ESMF, example code, and details of the API (Application Programming Interface).

Instructions on how to download the ESMPy code can be found at the ESMPy Download page.

Installing ESMPy

Installation of ESMPy requires a pointer to a file named inside of an ESMF installation. This file resides in a directory which looks like:


If the ESMFMKFILE flag is set when building ESMPy then it will not need to be referenced again. If not, an environment variable of the same name must be set with the path to the file every time that a new shell is initiated.

The ESMPy build can be installed in a custom location using the --prefix, --home, or --install-base flags to the install command. If this is done, then this location needs to be added to the PYTHONPATH environment variable in the user’s shell every time that a new shell is initiated. If a customized install location is not specified, ESMPy will be installed in the standard Python package installation directory on that particular machine.


The ESMPy build does not have to be installed to be used. The PYTHONPATH environment variable can simply be pointed to the directory containing the ESMF module (esmf/src/addon/ESMPy/src from a default git clone) after the build command.

As usual, any command followed by --help should print out some information on what options are available.

An installation of ESMPy in the default location for Python packages can be done with the following command issued from the top level ESMPy directory:

  • default Python package installation:
python build --ESMFMKFILE=<> install
  • custom install location:
python build --ESMFMKFILE=<>

python install --prefix=<custom_install_location>

setenv PYTHONPATH <custom_install_location>/lib/\*/site_packages

Please contact with any questions or problems.

Anaconda Packages

ESMPy conda packages are available through the NESII channel:

conda install -c nesii esmpy

There are Python3 compatible development versions available through the conda-forge channel:

conda install -c nesii/label/dev-esmf -c conda-forge esmpy

Importing ESMPy

To use ESMPy in an external program, import it with:

import ESMF


The ESMPy testing is done with the nose package, both in serial and parallel. The nose commands are wrapped in the following ESMPy targets:

python test

python test_examples

python test_regrid_from_file

python test_parallel

python test_examples_parallel

python test_regrid_from_file_parallel


The regrid_from_file tests can take up a lot of memory and bandwidth. The test_regrid_from_file_dryrun command will simply download the test files without actually running them (allowing the stress on the machine to be applied to bandwidth first, and then memory).

Alternatively, individual tests can be run with nose using the following format:

nosetests <file>:<test>


nosetests src/ESMF/test/test_api/


ESMPy doesn’t include many aspects of ESMF, including components, field bundles, time management, etc. The limitations listed here are relative to ESMF offline and integrated regridding capabilities.

  • ESMPy cannot use an ESMF installation that is built with external LAPACK support.
  • Coordinates cannot be retrieved from the elements of a Mesh. This can affect the ability to set Field values on a source Mesh created from file when using conservative regridding.
  • Multi-tile Grid support is limited to cubed-sphere grids created on 6 processors. A cubed-sphere grid can be created on any number of processors, but only when it is created on 6 processors will the coordinates be retrievable for the entire object.
  • There is no FieldBundle class, only single Fields.

Testing related:

  • Nightly regression testing is limited to a small subset of the ESMF test platforms, including Darwin and Linux running gfortran with openMPI.