Requirements & Installation


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Installing with pip

WebbPSF and its underlying optical library POPPY may be installed from the Python Package Index in the usual manner for Python packages.

$ pip install --upgrade webbpsf
[... progress report ...]

Successfully installed webbpsf

Note that pip install webbpsf only installs the program code. If you install via pip, you must manually download and install the data files, as described below. To obtain source spectra for calculations, you should also follow installation instructions for synphot.


Installation through conda is not available as of WebbPSF version 1.1.0. Conda users should instead follow the insructions in the preceding section to install via pip.

Installing or updating synphot

Stsynphot is an optional dependency, but is highly recommended. Its installation instructions can be found in the synphot docs or a discussion in the POPPY docs.

Installing the Required Data Files

If you install via pip or manually, you must install the data files yourself.

Files containing such information as the JWST pupil shape, instrument throughputs, and aperture positions are distributed separately from WebbPSF. To run WebbPSF, you must download these files and tell WebbPSF where to find them using the WEBBPSF_PATH environment variable.

  1. Download the following file: webbpsf-data-1.2.1.tar.gz [approx. 70 MB]

  2. Untar webbpsf-data-1.2.1.tar.gz into a directory of your choosing.

  3. Set the environment variable WEBBPSF_PATH to point to that directory. e.g.

    export WEBBPSF_PATH=$HOME/data/webbpsf-data

for bash. (You will probably want to add this to your .bashrc.)

You should now be able to successfully import webbpsf in a Python session.


If you have previously installed the data files for an earlier version of WebbPSF, and then update to a newer version, the software may prompt you that you must download and install a new updated version of the data files.


For STScI Users Only: Please note, we are no longer providing users at STScI a location with the required data files on the Central Storage network. Therefore, to run WebbPSF, you must download these files and tell WebbPSF where to find them using the WEBBPSF_PATH environment variable.

Software Requirements

See the requirements.txt specification file for the required package dependencies.

Required Python version: WebbPSF 1.1 and above require Python 3.9 or higher.

The major dependencies are the standard NumPy, SciPy, matplotlib stack, and Astropy.

Recommended Python packages:

  • synphot enables the simulation of PSFs with proper spectral response to realistic source spectra. Without this, PSF fidelity is reduced. See above for installation instructions for synphot. Stsynphot is recommended for most users.

Optional Python packages:

Some calculations with POPPY can benefit from the optional packages psutil and pyFFTW, but these are not needed in general. See the POPPY installation docs for more details. These optional packages are only worth adding for speed improvements if you are spending substantial time running calculations.

Additional packages are needed for the optional use of GPUs to accelerate calculations. See the POPPY documentation.

Installing a pre-release version or contributing to WebbPSF development

The WebbPSF source code repository is hosted at GitHub, as is the repository for POPPY. Users may clone or fork in the usual manner. Pull requests with code enhancements welcomed.

To install the current development version of WebbPSF, you can use pip to install directly from a git repository. To install WebbPSF and POPPY from git, uninstall any existing copies of WebbPSF and POPPY, then invoke pip as follows:

$ pip install -e git+ \
   -e git+

This will create directories ./src/poppy and ./src/webbpsf in your current directory containing the cloned repository. If you have commit access to the repository, you may want to clone via ssh with a URL like git+ssh:// Documentation of the available options for installing directly from Git can be found in the pip documentation.

Remember to install the required data files, if you have not already installed them.