Consider sharing CLAUDE.md (#7843)

CLAUDE.md

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+# Useful commands
+
+- `make pep8` — lint check
+- `make isort` — fix import ordering issues
+- `make format` — fix other Python source code formatting issues  
+- `mypy` — type check (no arguments; checks only files configured in `.mypy.ini`)
+
+
+# Guidelines
+
+- In addition to the directives in this document, also respect those contained
+  in `CONTRIBUTING.rst`
+
+- After making any code changes, always verify them with `make pep8` and `mypy` 
+
+- Don't worry about manually ordering imports. Instead, just run `make isort`
+
+- When extracting code out of a module covered by `mypy` into a new module,
+  remember to add the new module to `.mypy.ini`. Ask for confirmation before
+  making changes that would reduce `mypy` coverage
+
+- Remember that in `.mypy.ini`, there are two ways to configure a Python module
+  for coverage by `mypy`: *explicitly*, by listing its fully qualified module
+  path in the `modules` section of that file, or *implicitly*, by listing its
+  parent or ancestor package in the `packages` section
+
+- Prefer to use `git mv` when renaming or moving files
+
+- Do not commit any changes unless explicitly asked to do so. However, it's OK
+  to propose committing changes. When committing changes, include a trailer in 
+  the commit message that attributes the change to you
+
+- You can usually disregard any files under `attic/`, except for reference.
+  Never modify the attic, except when instructed to move files there.
+
+- Passing `--config-file .mypy.ini` to `mypy` is unnecessary; since `.mypy.ini` 
+  is the default config