Learning Discoveries

🧙‍♂️ Python: Learning Discoveries

Just a few notes on what I've learned while working on this project. I hope you find them useful!
Trying to get better about documentation in general but I'll keep this short and sweet.

🔮 Default Argument Evaluation

Patch Not Patching?

I was working on debugging a test for load_project_config in the Config class. The original code looked like this:

# ❌ BEWARE THIS SPELL! It contains hidden magic!
@staticmethod
def load_project_config(config_dir:Path = Path.cwd()) -> dict:
    """Load local project configuration"""
    local_config_path = config_dir / "canvas.json"
    if local_config_path.exists():
        with open(local_config_path, "r") as f:
            return json.load(f)
    else:
        return None

When you try to test this function by patching Path.cwd(), your test mysteriously fails! Why?

Argument Evaluation in Python

In Python, default arguments are evaluated ONCE at function definition time, not each time the function is called!

This means Path.cwd() is executed when the Python interpreter first reads your code - long before your patch is applied!

🌟 The Solution

Always use None as your default value when the default involves a function call, then evaluate inside the function:

# ✅ THE PROPER INCANTATION:
@staticmethod
def load_project_config(config_dir: Path = None) -> dict:
    """Load local project configuration"""
    if config_dir is None:
        config_dir = Path.cwd()  # Only now is Path.cwd() called!

    ...

Now your magical tests can properly patch Path.cwd() because it gets called each time the function runs!

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Local Github Actions w/ Act

What Is My GitHub Actions Workflow Gonna Do?

Act is a tool that allows you to run GitHub Actions locally. It simulates the GitHub Actions environment on your local machine, making it easier to test and debug workflows before pushing them to GitHub.

How Do I Use Act?

act -W .github/workflows/your_workflow.yml --artifact-server-path ./artifacts

• -W specifies the workflow file to run
• --artifact-server-path specifies the directory to store artifacts generated during the workflow run

This command will run the specified workflow and store any artifacts in the ./artifacts directory.
You can then inspect the artifacts to verify that the workflow ran as expected.

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