Uncaught FileNotFoundError when pip3 not found (pure UV environments)

[andylizf]

When using SkyPilot in an environment with UV instead of pip3, the wheel building process fails with an uncaught FileNotFoundError instead of the expected CalledProcessError.

  File "/home/andy/Power-RAG/.venv/lib/python3.10/site-packages/sky/backends/cloud_vm_ray_backend.py", line 2834, in _provision
    local_wheel_path, wheel_hash = wheel_utils.build_sky_wheel()
  File "/home/andy/Power-RAG/.venv/lib/python3.10/site-packages/sky/backends/wheel_utils.py", line 179, in build_sky_wheel
    latest_wheel = _build_sky_wheel()
  File "/home/andy/Power-RAG/.venv/lib/python3.10/site-packages/sky/backends/wheel_utils.py", line 103, in _build_sky_wheel
    subprocess.run([
  File "/home/andy/.local/share/uv/python/cpython-3.10.16-linux-x86_64-gnu/lib/python3.10/subprocess.py", line 503, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/home/andy/.local/share/uv/python/cpython-3.10.16-linux-x86_64-gnu/lib/python3.10/subprocess.py", line 971, in __init__
    self._execute_child(args, executable, preexec_fn, close_fds,
  File "/home/andy/.local/share/uv/python/cpython-3.10.16-linux-x86_64-gnu/lib/python3.10/subprocess.py", line 1863, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'pip3'

That's because the following code tries to run pip3 wheel but doesn't properly catch the error when pip3 is missing entirely:

skypilot/sky/backends/wheel_utils.py

Lines 100 to 113 in a9e9cf6

	try:
	# TODO(suquark): For python>=3.7, 'subprocess.run' supports capture
	# of the output.
	subprocess.run([
	'pip3', 'wheel', '--no-deps', norm_path, '--wheel-dir',
	str(tmp_dir)
	],
	stdout=subprocess.DEVNULL,
	stderr=subprocess.PIPE,
	check=True)
	except subprocess.CalledProcessError as e:
	raise RuntimeError('Failed to build pip wheel for SkyPilot. '
	f'Error message: {e.stderr.decode()}') from e

A quick fix is to add FileNotFoundError to the except block, like:

try:
    subprocess.run([...])
except (subprocess.CalledProcessError, FileNotFoundError) as e:
    if isinstance(e, FileNotFoundError):
        msg = "pip3 not found. Please install pip3."
    else:
        msg = f'Error message: {e.stderr.decode()}'
    raise RuntimeError('Failed to build pip wheel for SkyPilot. ' + msg) from e

We should further consider adding support for UV-only environments by checking for both pip3 and UV availability.

[cg505]

We should make this work in a full uv env. We can

1. Depend on pip to make sure it's installed.
2. If needed, use python -m pip to avoid any PATH issues.