Lazy help page

[relativityhd]

Right now, when doing --help on a lazy registered command or on an app containing lazy registered commands, the respective modules will be imported. This leads to a decreased user experience when exploring a CLI and it's commands when heavy dependencies, e.g. PyTorch, are used.

Pythons ast module could help with that, by only parsing a module's content when calling "--help" or "--version" and their variants. The ast representation includes docstrings and type annotations, so it should include everything needed to create the usage string.

Here is a quick example on how to extract the docstring and arguments from the AST:

# heavymodule.py
import torch


def myfunc(x: torch.Tensor) -> torch.Tensor:
    """Return the doubled tensor.

    Args:
        x (torch.Tensor): Input tensor.

    Returns:
        torch.Tensor: Output tensor with values doubled.

    """
    return x * 2

import ast
import importlib
import pathlib

import_path = "heavymodule:myfunc"
module_path, _, attr_path = import_path.rpartition(":")
# get the path of heavymodule.py and read its content
module_file = pathlib.Path(importlib.util.find_spec(module_path).origin)
module_code = module_file.read_text()
module_tree = ast.parse(module_code)

for node in module_tree.body:
    if isinstance(node, ast.FunctionDef) and node.name == attr_path:
        func_node = node
        break
print(f"=== Functions AST:\n{ast.dump(func_node)}")
print(f"=== Functions docstring:\n{func_node.body[0].value.value}")
print(f"=== Functions attributes as AST:\n{ast.dump(func_node.args)}")

[BrianPugh]

Related: #675; just take this into consideration depending on how much effort/work this will take.