uv pip compile --universal not picking up required transitive dependency for certain python versions

[brendan-morin]

Summary

Overview

I'm seeing some weird behavior where uv pip compile --universal does not seem to properly resolve the async-timeout transitive dependency of aiohttp, which is only required for python < 3.11. We can see this dep listed here.

It does seem to work if --python-version is specified to a lower version (despite warning it doesn't exist), though this doesn't seem to be the intended outcome reading the docs/help strings for --universal and --python-version.

Repro

uv.toml

python-install-mirror = "https://..." # Internal mirror
python-preference = "managed"

[[index]]
url = internal index
default = true
native-tls = true

requirements.in

aiohttp==3.11.11

Commands:

uv pip compile --universal requirements.in

Output:

Resolved 9 packages in 10ms
# This file was autogenerated by uv via the following command:
#    uv pip compile --universal requirements.in
aiohappyeyeballs==2.4.4
    # via aiohttp
aiohttp==3.11.11
    # via -r requirements/test.in
aiosignal==1.3.2
    # via aiohttp
attrs==25.1.0
    # via aiohttp
frozenlist==1.5.0
    # via
    #   aiohttp
    #   aiosignal
idna==3.10
    # via yarl
multidict==6.1.0
    # via
    #   aiohttp
    #   yarl
propcache==0.2.1
    # via
    #   aiohttp
    #   yarl
yarl==1.18.3
    # via aiohttp

versions:

uv --version

> uv 0.5.29 (ca73c4754 2025-02-05)

python --version

> Python 3.11.8

Note that running using --python 3.10 provides a warning that it does not exist, but provides the expected output below now: async-timeout==5.0.1 ; python_full_version < '3.11'

uv pip compile --universal --python-version 3.10 requirements.in
warning: The requested Python version 3.10 is not available; 3.11.8 will be used to build dependencies instead.
Resolved 11 packages in 5ms
# This file was autogenerated by uv via the following command:
#    uv pip compile --universal --python-version 3.10  requirements.in
aiohappyeyeballs==2.4.4
    # via aiohttp
aiohttp==3.11.11
    # via -r requirements/test.in
aiosignal==1.3.2
    # via aiohttp
async-timeout==5.0.1 ; python_full_version < '3.11'
    # via aiohttp
attrs==25.1.0
    # via aiohttp
frozenlist==1.5.0
    # via
    #   aiohttp
    #   aiosignal
idna==3.10
    # via yarl
multidict==6.1.0
    # via
    #   aiohttp
    #   yarl
propcache==0.2.1
    # via
    #   aiohttp
    #   yarl
typing-extensions==4.12.2 ; python_full_version < '3.11'
    # via multidict
yarl==1.18.3
    # via aiohttp

Cargo culting

One more note, and take this with a grain of salt, but I am 80% sure it initially did not resolve the transitive dep when using--python-version 3.10, but then after removing python-preference = "managed" from my uv.toml and then rerunning, it seemed to now work (though I am unable to reproduce that behavior now). I am only including this in case it is somehow related to existing uv python versions on the system.

Platform

macOS

Version

uv 0.5.29 (ca73c47 2025-02-05)

Python version

Python 3.11.8

[charliermarsh]

If you don't specify a --python-version, I believe we'll use the discovered Python as the minimum supported version. So, in this case, it looks like we're resolving for Python 3.11.8 and later -- in which case, async-timeout can be omitted, since it's never relevant on those versions!

[brendan-morin]

I think that’s sensible enough. Maybe more of a documentation fix then, the cli help doesn’t seem to imply this limitation.

[zanieb]

We do have this in the documentation

❯ uv help pip compile | grep "default minimum Python" -B 8

Python options:
      --python <PYTHON>
          The Python interpreter to use during resolution.
          
          A Python interpreter is required for building source distributions to
          determine package metadata when there are not wheels.
          
          The interpreter is also used to determine the default minimum Python

and

❯ uv help pip compile | grep "\-\-universal" -A 4
      --universal
          Perform a universal resolution, attempting to generate a single `requirements.txt` output file that is compatible
          with all operating systems, architectures, and Python implementations.
          
          In universal mode, the current Python version (or user-provided `--python-version`) will be treated as a lower
          bound. For example, `--universal --python-version 3.7` would produce a universal resolution for Python 3.7 and
          later.
          
          Implies `--no-strip-markers`.

[brendan-morin]

Interesting, it looks like maybe the --help docs are out of sync with the uv help docs? Or perhaps just an unfortunate caveat cut off from concise vs detailed docs.

> uv pip compile --help | grep "default minimum Python" -B 8 

> uv pip compile --help | grep "\-\-universal" -A 4
      --universal                                        Perform a universal resolution, attempting to generate a single `requirements.txt` output file that is
                                                         compatible with all operating systems, architectures, and Python implementations
      --no-emit-package <NO_EMIT_PACKAGE>                Specify a package to omit from the output resolution. Its dependencies will still be included in the
                                                         resolution. Equivalent to pip-compile's `--unsafe-package` option
      --emit-index-url                                   Include `--index-url` and `--extra-index-url` entries in the generated output file