Format with Black and Flake8

[rexwangcc]

Purpose

Please explain the purpose of this PR and include links to any GitHub issues that it fixes:

• https://broadinstitute.atlassian.net/jira/software/projects/GH/boards/530?selectedIssue=GH-128

  Changes

  Please list out what major changes were made in this PR to address the issue:

• Format the code base with Black.

  Review Instructions

  Please provide instructions about how should a reviewer test/verify the changes in this PR:

• Please check if the 2 tests (linting + unit) are both passing.

• Please check if there are any deal-breakers that Black provides here, for instance:

  • Do you think it's OK to always add () everywhere? Black adds them almost everywhere.
  • Do you think it's OK to have extra lines?
  • Do you think it's OK to always dedent the closing brackets and add a trailing comma? Black does that to produce smaller diffs in code reviews.
  • etc.