feat: default python read from .python-version-default or .python-ver…

…sion file

changelog.d/20241231_083257_william.krekelberg.md

@@ -0,0 +1,45 @@
+<!-- markdownlint-disable MD041 -->
+<!--
+A new scriv changelog fragment.
+
+Uncomment the section that is right (remove the HTML comment wrapper).
+-->
+
+<!--
+### Removed
+
+- A bullet item for the Removed category.
+
+-->
+<!--
+### Added
+
+- A bullet item for the Added category.
+
+-->
+
+### Changed
+
+- Read default version from first found file, in order,
+  `.python-version-default` and `.python-version`. This allows for "default"
+  version being different from pinned version specifier, as the latter can be a
+  range of python values.
+
+<!--
+### Deprecated
+
+- A bullet item for the Deprecated category.
+
+-->
+<!--
+### Fixed
+
+- A bullet item for the Fixed category.
+
+-->
+<!--
+### Security
+
+- A bullet item for the Security category.
+
+-->

src/pyproject2conda/cli.py

@@ -267,13 +267,14 @@ class Overwrite(str, Enum):
         `--python-version={version} --python-include=python{version}`. if
         passed, this overrides values of passed via `--python-version` and
         `--python-include`. pass `--python="default"` to include the python
-        version (major.minor only) from `.python-version` file in the current
-        directory. pass `"lowest"` or `"highest"` to include the lowest or
-        highest python version, respectively, from
-        `pyproject.toml:project.classifiers` table. in project mode, you can
-        pass multiple python version in `pyproject.toml` with, e.g., `python =
-        ["3.8", "3.9", ....]`, or using `python = "all"`, to include all python
-        versions extracted from `pyproject.toml:project.classifiers` table.
+        version (major.minor only) from, in order, `.python-version-default` or
+        `.python-version`file in the current directory. pass `"lowest"` or
+        `"highest"` to include the lowest or highest python version,
+        respectively, from `pyproject.toml:project.classifiers` table. in
+        project mode, you can pass multiple python version in `pyproject.toml`
+        with, e.g., `python = ["3.8", "3.9", ....]`, or using `python = "all"`,
+        to include all python versions extracted from
+        `pyproject.toml:project.classifiers` table.
         """,
     ),
 ]

src/pyproject2conda/config.py

@@ -12,7 +12,7 @@
 from pyproject2conda.utils import (
     filename_from_template,
     get_all_pythons,
-    get_default_pythons,
+    get_default_pythons_with_fallback,
     get_in,
     select_pythons,
 )
@@ -459,7 +459,7 @@ def from_toml_dict(
 
         c = cls(
             data,
-            default_pythons=get_default_pythons(),
+            default_pythons=get_default_pythons_with_fallback(),
             all_pythons=get_all_pythons(data_toml),
         )
 

src/pyproject2conda/utils.py

@@ -80,6 +80,18 @@ def get_default_pythons(path: str | Path = ".python-version") -> list[str]:
     return []
 
 
+def get_default_pythons_with_fallback(
+    paths: Iterable[str | Path] = (".python-version-default", ".python-version"),
+) -> list[str]:
+    """Get default pythons from possibly multiple sources"""
+    for path in paths:
+        out = get_default_pythons(path)
+        if len(out) > 0:
+            return out
+
+    return []
+
+
 def get_all_pythons(
     data: dict[str, Any] | None, path: str | Path | None = None
 ) -> list[str]:
@@ -120,7 +132,7 @@ def select_pythons(
 
         if python == "default":
             if not default_pythons:
-                msg = "Must include `.python-version` to use `python = 'default'`."
+                msg = "Must include `.python-version-default` or `.python-version` to use `python = 'default'`."
                 raise ValueError(msg)
             return default_pythons
 

tests/test_config.py

@@ -345,17 +345,43 @@ def test_option_override_base3_default_python_error(
     simple_config: Config,
 ) -> None:
     # using default python without a version
-    with pytest.raises(ValueError, match="Must include `.python-version` .*"):
+    with pytest.raises(
+        ValueError,
+        match="Must include `.python-version-default` or `.python-version`.*",
+    ):
         list(simple_config.iter_envs(envs=["base3"]))
 
 
+@pytest.mark.parametrize(
+    ("python_version_default", "python_version", "expected"),
+    [
+        (None, None, []),
+        (None, "3.10", ["3.10"]),
+        ("3.12", "3.11", ["3.12"]),
+        ("3.11", None, ["3.11"]),
+    ],
+)
+def test_default_pythons(
+    example_path, python_version_default, python_version, expected
+) -> None:
+    for name, version in zip(
+        [".python-version-default", ".python-version"],
+        [python_version_default, python_version],
+    ):
+        if version is not None:
+            with (example_path / name).open("w") as f:
+                f.write(f"{version}\n")
+
+    assert utils.get_default_pythons_with_fallback() == expected
+
+
 def test_option_override_base3_default_python(example_path, simple_toml: str) -> None:
-    with (example_path / ".python-version").open("w") as f:
+    with (example_path / ".python-version-default").open("w") as f:
         f.write("3.10\n")
 
-    from pyproject2conda.utils import get_default_pythons
+    from pyproject2conda.utils import get_default_pythons_with_fallback
 
-    assert get_default_pythons() == ["3.10"]
+    assert get_default_pythons_with_fallback() == ["3.10"]
 
     config = Config.from_string(dedent(simple_toml))
     output = list(config.iter_envs(envs=["base3"]))