Compare two models#

Diff two model files so that the diff shows only what the models mean differently. A plain text diff also shows the order of declarations, spacing and the order of the terms in a sum. The canonical form removes those differences. Comparing two models lists what the form sorts and what it keeps.

1. Write one model in the canonical form.

python -m mathspec canonical model.yaml

The form goes to stdout. -o canonical.yaml writes it to a file instead. A file the language refuses prints its message on stderr and exits with status 1.

2. Diff two files once. Give each file to the command, and diff the two outputs:

diff <(python -m mathspec canonical before.yaml) <(python -m mathspec canonical after.yaml)

3. Make git diff show the canonical form. Tell git which files are models, and which command writes them out:

echo 'models/*.yaml diff=mathspec' >> .gitattributes
git config diff.mathspec.textconv "python -m mathspec canonical"

The files in the repository stay as you wrote them. Only the diff changes. A commit that writes sum(dispatch * cost) as sum(cost * dispatch) shows no difference. A commit that changes a coefficient shows one line:

 objective:
   sense: minimize
-  expression: sum(cost * dispatch)
+  expression: sum((2 * cost) * dispatch)

Match only model files in .gitattributes. Git runs the command on every file the pattern matches, and a YAML file that is not a model fails to load.

4. Keep models in the canonical form in CI. Then the files themselves diff the way the form does, with no git setup. --write rewrites a file in the form. The form holds no YAML comments, so --write drops them:

python -m mathspec canonical --write model.yaml

--check writes nothing. It exits with status 1 if the file is not in the form, and names the rewrite:

model.yaml is not in the canonical form. Run `python -m mathspec canonical --write model.yaml` to rewrite it.

Check every model, and fail the job if one of them fails:

status=0
for model in models/*.yaml; do python -m mathspec canonical --check "$model" || status=1; done
exit $status

5. Compare from Python where the comparison is one step of a longer script. to_yaml writes the same text with canonical=True:

import mathspec as ms

before = ms.to_spec('before.yaml').to_yaml(canonical=True)
after = ms.to_spec('after.yaml').to_yaml(canonical=True)
print(before == after)