PyFoam problem - ImportError: No module named PyFoam

Question

I just install PyFoam using:

pip install PyFoam

Then I wrote a test.py file using:

import PyFoam

Now I got an error message:

    import PyFoam
ImportError: No module named PyFoam

Then I tried install again, and I got this:

pip install PyFoam
Requirement already satisfied: PyFoam in ./.local/lib/python3.8/site-packages (2021.6)
Requirement already satisfied: numpy in ./.local/lib/python3.8/site-packages (from PyFoam) (1.23.0)

Could anyone help? Tks.

Answer 1

The issue is likely that you use one version of pip and another version of the Python interpreter. This is particularly common if you have several Python installations on your system. Check that these versions match with each other.

For example, run

python --version
pip --verion

You should see output similar to the following:

Python 3.10.2
pip 22.1.2 from /Library/Frameworks/Python.framework/Versions/3.10/lib/python3.10/site-packages/pip (python 3.10)

Notice the matching version numbers. I am verifying this on my system with Homebrew, under MacOS, but I assume that it's similar on other systems. Here, different instances of "python" and "pip" binaries are suffixed with the version number. So, if your version of "pip" says "3.8", try specifying "python3.8" as interpreter.

It might also be helpful for troubleshooting to know of the "-m" switch, in order to locate a module. In your example, you would run:

python -mPyFoam

Notice the capitalization for this module, which can differ between the one being used to install the module through pip and when importing it. On my system, as an example, it outputs:

/Library/Frameworks/Python.framework/Versions/3.10/bin/python3: No module named PyFoam.__main__; 'PyFoam' is a package and cannot be directly executed

The error message is fine. It does still mean the module was found. That is in contrast to an output like the following:

/Library/Frameworks/Python.framework/Versions/3.10/bin/python3: No module named pyfoam

The -m switch is documented under https://peps.python.org/pep-0338/.

Another possibility might be that you need to check and configure your Python module search path, as described here https://docs.python.org/3/tutorial/modules.html.

When a module named spam is imported, the interpreter first searches for a built-in module with that name. These module names are listed in sys.builtin_module_names. If not found, it then searches for a file named spam.py in a list of directories given by the variable sys.path. sys.path is initialized from these locations:

The directory containing the input script (or the current directory when no file is specified).

PYTHONPATH (a list of directory names, with the same syntax as the shell variable PATH).

The installation-dependent default (by convention including a site-packages directory, handled by the site module).

Note On file systems which support symlinks, the directory containing the input script is calculated after the symlink is followed. In other words the directory containing the symlink is not added to the module search path. After initialization, Python programs can modify sys.path. The directory containing the script being run is placed at the beginning of the search path, ahead of the standard library path. This means that scripts in that directory will be loaded instead of modules of the same name in the library directory. This is an error unless the replacement is intended. See section Standard Modules for more information.

It's possible to try to think of other causes. But without any additional information about your setup it would probably be too speculative and become confusing for other people reading this answer, so I will leave it at these two causes, which I believe to be the most common for this type of issue.