fix a few flake8 warnings

[jameslamb]

Contributes to #161.

Changes

Fixes the following minor flake8 warnings.

./hamilton/graph.py:426:17: F841 local variable 'e' is assigned to but never used
./hamilton/base.py:121:17: F541 f-string is missing placeholders
./hamilton/base.py:129:17: F541 f-string is missing placeholders
./tests/test_function_modifiers.py:312:1: E266 too many leading '#' for block comment
./tests/test_function_modifiers.py:333:1: E266 too many leading '#' for block comment

Testing

pre-commit run --all-files

Notes

Thanks for your time and consideration.

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code can be automatically merged (no conflicts)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Passes all existing automated tests
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.
• Reviewers requested with the Reviewers tool ➡️

Testing checklist

Python - local testing

• python 3.6
• python 3.7