Use python if python3 is not available

.github/workflows/go.yml

@@ -18,8 +18,6 @@ jobs:
       uses: actions/setup-python@v5
       with:
         python-version: 3.8
-    - name: Install sphinx
-      run: pip install sphinx sphinx-rtd-theme sphinx-tabs
     - name: Checkout code
       uses: actions/checkout@v4
     - name: Bootstrap

.github/workflows/release.yml

@@ -16,8 +16,6 @@ jobs:
       uses: actions/setup-python@v5
       with:
         python-version: 3.8
-    - name: Install sphinx
-      run: pip install sphinx sphinx-rtd-theme
     - name: Checkout code
       uses: actions/checkout@v4
     - name: Run GoReleaser

docs/BUILD.dawn

@@ -4,8 +4,9 @@ def venv():
     Creates a venv for the docs build.
     """
 
-    sh.exec("python3 -m venv venv")
-    sh.exec(". venv/bin/activate && python3 -m pip install -r requirements.txt")
+    python = "python3" if os.look_path("python3") != None else "python"
+    sh.exec(f"{python} -m venv venv")
+    sh.exec(f". venv/bin/activate && {python} -m pip install -r requirements.txt")
 
 @target(deps=[venv], sources=os.glob(["../README.rst", "source/**", "conf.py"]), generates=["build"])
 def site():

docs/source/modules/os.rst

@@ -24,6 +24,18 @@
    the process environment. This mapping is captured at startup time.
 
 
+.. py:function:: look_path(file)
+
+   Search for an executable named file in the directories named by
+   the PATH environment variable. If file contains a slash, it is
+   tried directly and the PATH is not consulted. Otherwise, on
+   success, the result is an absolute path.
+
+   :param file: the name of the executable to find
+
+   :returns: the absolute path to file if found or None if not found.
+
+
 .. py:function:: exec(command, cwd=None, env=None, try_=None)
 
    Run an executable. If the process fails, the calling module will

lib/os/exec.go

@@ -10,6 +10,31 @@ import (
 	"go.starlark.net/starlark"
 )
 
+// def look_path(file):
+//     """
+//     Search for an executable named file in the directories named by
+//     the PATH environment variable. If file contains a slash, it is
+//     tried directly and the PATH is not consulted. Otherwise, on
+//     success, the result is an absolute path.
+//
+//     :param file: the name of the executable to find
+//
+//     :returns: the absolute path to file if found or None if not found.
+//     """
+//
+//starlark:builtin factory=NewLookPath,function=LookPath
+func lookPath(
+	thread *starlark.Thread,
+	fn *starlark.Builtin,
+	file string,
+) (starlark.Value, error) {
+	path, err := exec.LookPath(file)
+	if err != nil {
+		return starlark.None, nil
+	}
+	return starlark.String(path), nil
+}
+
 // def exec(command, cwd=None, env=None, try_=None):
 //     """
 //     Run an executable. If the process fails, the calling module will

lib/os/module.go

@@ -24,6 +24,10 @@ import (
 //     def environ():
 //         pass
 //
+//     @function("lookPath")
+//     def look_path():
+//         pass
+//
 //     @function("execf")
 //     def exec():
 //         pass
@@ -58,13 +62,14 @@ var Module = &starlarkstruct.Module{
 	Members: starlark.StringDict{
 		"path": path.Module,
 
-		"environ":  NewEnviron(),
-		"exec":     NewExec(),
-		"output":   NewOutput(),
-		"exists":   NewExists(),
-		"getcwd":   NewGetcwd(),
-		"glob":     NewGlob(),
-		"mkdir":    NewMkdir(),
-		"makedirs": NewMakedirs(),
+		"environ":   NewEnviron(),
+		"look_path": NewLookPath(),
+		"exec":      NewExec(),
+		"output":    NewOutput(),
+		"exists":    NewExists(),
+		"getcwd":    NewGetcwd(),
+		"glob":      NewGlob(),
+		"mkdir":     NewMkdir(),
+		"makedirs":  NewMakedirs(),
 	},
 }