How can I fix the ImportError for pywrapgraph in OR-Tools using a conda environment?

Below is a list of troubleshooting steps and suggestions that have helped others resolve similar import issues with OR-Tools in a conda environment:

1. Confirm the Installation

Sometimes multiple installations (e.g. conda vs. pip) can cause conflicts. Verify that the installed version of OR-Tools is the one you expect:

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pip show ortools

Make sure it’s the latest version and note its installation path.

2. Remove and Reinstall OR-Tools

If there’s any doubt about a corrupted installation, try uninstalling and reinstalling OR-Tools:

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pip uninstall ortools
pip install ortools

You can also force a reinstall:

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pip install --upgrade --force-reinstall ortools

3. Check for Conflicting Module Names

Sometimes a local file or directory named “ortools” (or similar) can inadvertently shadow the installed package. Ensure that you haven’t named your script or any local modules “ortools.py” or “graph.py.”

4. Use the Correct Import

For graph optimization, the correct way to import should be:

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from ortools.graph import pywrapgraph

Double-check your source code to ensure there’s no typo or conflicting module that might be imported instead of the OR-Tools one.

5. Consider Environment Distribution

While pip works well in many cases, using conda-forge to install OR-Tools in a conda environment is sometimes more reliable:

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conda install -c conda-forge ortools

This ensures that dependencies (especially related to binary files) match your conda environment.

6. Verify Runtime Dependencies

OR-Tools includes precompiled binaries that on Windows often need Microsoft Visual C++ Redistributable packages. Make sure that these runtime libraries are installed on your system.

7. Run a Minimal Check

After reinstalling, try running a minimal script from the command line to verify:

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# test_ortools.py
from ortools.graph import pywrapgraph

def main():
    print("Successfully imported pywrapgraph!")

if __name__ == '__main__':
    main()

Then run:

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python test_ortools.py

If this minimal check fails with the same error, then the issue is likely with the build/distribution rather than your code.

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These steps address the most common causes of the error you described. If you still encounter the error after these troubleshooting steps, consider sharing details (like OS version, Python version, and the exact steps you followed) as this information can help further narrow down the root cause.