Create main.py instead of hello.py in uv init

[Gankra]

Initially it seemed like app.py might be slightly more desirable but people seem to overwhelmingly favour main.py as a good "generic" name.

Fixes #7782

[Gankra]

The only concern I have with this is it changes intro docs, so there will be an awkward period where people have older versions of uv that make hello.py but the guide says they make app.py. Dunno if we want to make the docs hedge for a bit or what.

[zanieb]

The only concern I have with this is it changes intro docs, so there will be an awkward period where people have older versions of uv that make hello.py but the guide says they make app.py. Dunno if we want to make the docs hedge for a bit or what.

I'd just go for it — you could add an admonition about older versions if you want though.

[zanieb]

Arguably this is sort of breaking, though I'm not sure we consider uv init to be a typical programmatic interface. @charliermarsh thoughts?

If we decide it's breaking, we'll just hold it until 0.6.0 (for which there is a milestone to track other breaking changes).

[charliermarsh]

It probably makes sense to defer this to v0.6. We could do a v0.6 in the near future though.

[zanieb]

Sorry for giving you an unmergable task!

[Bengt]

1. For reference,

• there are currently 50.700 hello.py files on GitHub,
• there are currently 132.000 cli.py files on GitHub, and
• there are currently 175.000 example.py files on GitHub.

2. In Python, default file names vary a bit with the domain, and hence one's expectations might be shaped in various ways. app.py is indeed common, with currently about 721.000 app.py files on GitHub.

3. Still, main.py is an even more common name. At the time of writing, there are 2.2 million main.py files on GitHub. Interestingly, this is exactly because 'main' is a commonly used name in the Python world, like main(), __main__, or __main__.py. To adhere to this pythonic naming scheme and avoid surprises, main.py should in my opinion be default in uv init.

4. I do not feel like there is one, universally accepted best practice for naming your first file. I think we would therefore need a command line argument for naming the default file. The command line option should also include a way to disable creating a default file altogether. Currently, one needs to advise uv init && rm hello.py, which seems unnecessarily convoluted and is not portable to PowerShell, so portable instructions require duplication. m(

5. The default file is handy if one starts from scratch, but cumbersome if there is an existing codebase. With an existing code base, the use case is to introduce uv to it, not build something new. In projects with preexisting code, uv would ideally detect the presence of a codebase and not create a default file. This should be equivalent to using the deactivation functionality mentioned in 4.

[Gankra]

Wow, thanks for all the great insight! That all seems pretty agreeable.

[zanieb]

We are already tracking (5) in #6750

[charliermarsh]

It seems like FastAPI generally recommends main.py, at least here, though in my testing fastpi dev auto-detects both main.py and app.py (but not hello.py). Here's the full list: https://github.com/fastapi/fastapi-cli/blob/9a4741816dc288bbd931e693166117d98ee14dea/src/fastapi_cli/discover.py#L19-L26.

On the other hand, it looks like Flask auto-detects app.py, but not main.py (https://flask.palletsprojects.com/en/stable/cli/).

[Kludex]

main is far better choice than any alternative. Good job.

[zanieb]

:D thanks Marcelo