Implement the CLI with Click instead of argparse

[csadorf]

Summary

Implement the command line interface (CLI) with the Click library instead of argparse.

Motivation

Using Click for the implementation of a CLI has numerous advantages over using argparse, including a more concise API, the enforcement of a more consistent interface, and built-in support for the implementation of test runners. In addition, the library comes with a collection of helper functions and tools, that are relevant for CLI development. Please see this page for a more comprehensive overview of why one would want to implement a CLI with Click.

Proposed plan for implementation

Since this is a larger refactoring project, it should be executed in stages. Each stage should be introduced as a separate pull request:

• Ensure that the coverage of signac/__main__.py is measured, see instructions here.
• Review existing unit tests for signac/__main_.py and implement missing tests to reach a test coverage of at least 80%.
• Refactor the CLI implementation, replacing argparse with Click exclusively for the 'find' sub command; mark all unit tests for other sub-commands as expected failures. Once the find sub-command was successfully refactored, refactor all other sub-commands. Replicate the unit tests for each command found in tests/test_shell.py in a seperate test module called tests/test_main.py with Click's built-in test runner. The original tests may not fail!

Risks

It is very likely that not all sub-commands can be implemented in the exact same way as before, because Click imposes some restrictions that argparse does not. These restrictions will likely improve the consistency and quality of the CLI, but make it a bit more difficult to create an exact replacement and may require the introduction of some minor backwards incompatibilities.

[csadorf]

@vishav1771 Would you be interested in giving this a shot?

[vishav1771]

Sure 👍

[csadorf]

Sure

Awesome, thx! Please feel free to discuss questions about this project directly on this issue. Please apply the "Click" label to any PRs related to this issue so that it is easier for us to keep track of things.

[bdice]

@vishav1771 Thanks for taking this on! Eventually we will want to do the same for signac-flow, so it may be helpful to document the steps you take along the way for a contributor to do this again for that package.

[vishav1771]

To measure coverage of signac/__main__.py: pytest provides pytest-cov extension which can be used. Should I go with this?

[vyasr]

I think using pytest-cov is a good idea. We will probably want to use click.testing for actually writing future tests.

[csadorf]

I unlinked #300 again, because merging that PR will not fully close this issue.

[csadorf]

I've marked the first two tasks as completed with the merge of #300 . Nice job @vishav1771 !

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.