`uv init` hangs forever unless I add `--python-preference only-managed`

[will-henney]

Hi,

Just trying out uv for the first time (previous experience with rye), and weirdly I ran into problems running the first example command in the Getting Started docs:

$ uv -v init example
DEBUG uv 0.4.15
DEBUG Searching for default Python interpreter in managed installations or system path
DEBUG Searching for managed installations at `.local/share/uv/python`

and it just hangs forever until killed, using almost no CPU resources.

I guessed it was a problem with the search for pre-existing local python installations, so I tried it with

$ uv -v init example --python-preference only-managed

and that works fine.

System is macOS Sonoma 14.2.1 (23C71) running on intel

$ uv --version
uv 0.4.15 (0d81bfbc6 2024-09-21)

$ uname -a
Darwin gris.local 23.2.0 Darwin Kernel Version 23.2.0: Wed Nov 15 21:54:10 PST 2023; root:xnu-10002.61.3~2/RELEASE_X86_64 x86_64

Thanks

Will

[zanieb]

That's really weird — can you share the output of RUST_LOG=uv=trace uv python find -v?

[will-henney]

So, now that I have run once with only-managed it seems to be working fine even without that flag. I get

$ RUST_LOG=uv=trace uv python find -v
DEBUG uv 0.4.15
DEBUG Searching for default Python interpreter in managed installations or system path
DEBUG Searching for managed installations at `/Users/will/.local/share/uv/python`
DEBUG Found managed installation `cpython-3.12.6-macos-x86_64-none`
TRACE Cached interpreter info for Python 3.12.6, skipping probing: /Users/will/.local/share/uv/python/cpython-3.12.6-macos-x86_64-none/bin/python3
DEBUG Found `cpython-3.12.6-macos-x86_64-none` at `/Users/will/.local/share/uv/python/cpython-3.12.6-macos-x86_64-none/bin/python3` (managed installations)
/Users/will/.local/share/uv/python/cpython-3.12.6-macos-x86_64-none/bin/python3

However, if I try and get back to the initial conditions after installing uv for the first time by nuking .local/share/uv, then I can reproduce the hanging behavior:

$ rm -r ~/.local/share/uv
$ RUST_LOG=uv=trace uv python find -v
DEBUG uv 0.4.15
DEBUG Searching for default Python interpreter in managed installations or system path
DEBUG Searching for managed installations at `/Users/will/.local/share/uv/python`
TRACE Searching PATH for executables: python3, python
TRACE Checking `PATH` directory for interpreters: /Users/will/.cargo/bin
TRACE Checking `PATH` directory for interpreters: /Users/will/.gem/ruby/2.6.0/bin
TRACE Checking `PATH` directory for interpreters: /Users/will/mambaforge/condabin
TRACE Checking `PATH` directory for interpreters: /Users/will/.rye/shims
TRACE Found possible Python executable: /Users/will/.rye/shims/python3
TRACE Querying interpreter executable at /Users/will/.rye/shims/python3
^C

So it looks like the problem might be with the rye-installed python. I will check this next

[zanieb]

I wonder if the Rye shim is invoking uv so it cycles?

[will-henney]

Could be ...

$ ls -l /Users/will/.rye/shims/python3
lrwxr-xr-x  1 will  staff  26 Aug 14 13:17 /Users/will/.rye/shims/python3 -> /Users/will/.rye/shims/rye

$ rye --version
rye 0.38.0
commit: 0.38.0 (3e3c8540f 2024-08-02)
platform: macos (x86_64)
self-python: cpython@3.12.1
symlink support: true
uv enabled: true

I did rye self update so it is now on 0.39.0 but that did not help

[bluss]

Could you run the rye shim (in the same directory as previous experiments) and print(sys.executable)

[will-henney]

OK, we seem to be getting somewhere. It turns out that the rye shim hangs when I try to run it outside of any rye or uv managed project. So this explains the uv init hangs

Looking at the rye docs, it seems that it should be finding the system python in this case, which I guess is the part that seems to be broken on my machine.

If I do

$ rye config --set-bool behavior.global-python=true

then the shim now does work in non-managed directories:

# will @ gris in ~/tmp [10:46:53]
$ /Users/will/.rye/shims/python
Python 3.12.1 (main, Jan  8 2024, 06:38:22) [Clang 16.0.3 ] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys; print(sys.executable)
/Users/will/.rye/py/cpython@3.12.1/install/bin/python3

and uv init now works fine, even starting from an empty ~/.local/share/uv folder:

$ uv -v init example-4
DEBUG uv 0.4.16
DEBUG Searching for default Python interpreter in managed installations or system path
DEBUG Searching for managed installations at `/Users/will/.local/share/uv/python`
DEBUG Found `cpython-3.12.1-macos-x86_64-none` at `/Users/will/.rye/shims/python` (search path)
DEBUG Writing Python versions to `/Users/will/tmp/example-4/.python-version`
Initialized project `example-4` at `/Users/will/tmp/example-4`

Oddly, this now seems to be picking up a homebrew version of python

$ (cd example-4; uv run hello.py)
Using CPython 3.12.4 interpreter at: /usr/local/opt/python@3.12/bin/python3.12
Creating virtual environment at: .venv
Hello from example-4!

Then I double-checked by running

rye config --set-bool behavior.global-python=false
mv ~/.local/share/uv/python ~/.local/share/uv/python-MOVED
uv -v init example-6

and that reproduced the hang again.