Python: Add vendor directory to the path automatically if present

This won't work yet with top level imports from the vendor directory
because of snapshot problems. I am leaving that to a followup.

src/pyodide/internal/python.ts

@@ -110,6 +110,18 @@ export async function loadPyodide(
     (msg) => console.log(msg),
     (msg) => console.error(msg)
   );
+  pyodide.runPython(`
+    def _tmp():
+      import sys
+      from pathlib import Path
 
+      VENDOR_PATH = "/session/metadata/vendor"
+      print(VENDOR_PATH, Path(VENDOR_PATH).is_dir())
+      if Path(VENDOR_PATH).is_dir():
+        sys.path.append(VENDOR_PATH)
+
+    _tmp()
+    del _tmp
+  `);
   return pyodide;
 }

src/pyodide/types/Pyodide.d.ts

@@ -8,6 +8,7 @@ interface PyModule {
 
 interface Pyodide {
   _module: Module;
+  runPython: (code: string) => void;
   registerJsModule: (handle: string, mod: object) => void;
   pyimport: (moduleName: string) => PyModule;
   FS: FS;

src/workerd/server/tests/python/BUILD.bazel

@@ -78,10 +78,13 @@ py_wd_test("seek-metadatafs")
 py_wd_test(
     "undefined-handler",
     # TODO: Requires a new bundle deploy
-    skip_python_flags = [
-        "0.26.0a2",
-        "0.27.1",
-    ],
+    python_flags = ["development"],
+)
+
+py_wd_test(
+    "vendor_dir",
+    # TODO: Requires a new bundle deploy
+    python_flags = ["development"],
 )
 
 py_wd_test("dont-snapshot-pyodide")

src/workerd/server/tests/python/vendor_dir/vendor/a.py

@@ -0,0 +1 @@
+A = 77

src/workerd/server/tests/python/vendor_dir/vendor_dir.wd-test

@@ -0,0 +1,16 @@
+using Workerd = import "/workerd/workerd.capnp";
+
+const unitTests :Workerd.Config = (
+  services = [
+    ( name = "vendor_dir",
+      worker = (
+        modules = [
+          (name = "worker.py", pythonModule = embed "worker.py"),
+          (name = "vendor/a.py", pythonModule = embed "vendor/a.py")
+        ],
+        compatibilityDate = "2024-01-15",
+        compatibilityFlags = [%PYTHON_FEATURE_FLAGS],
+      )
+    ),
+  ],
+);

src/workerd/server/tests/python/vendor_dir/worker.py

@@ -0,0 +1,4 @@
+def test():
+    from a import A
+
+    assert A == 77