another attempt

Author: iskakaushik

tools/fuchsia/dart/vpython3.txt

@@ -0,0 +1,5 @@
+python_version: "3.8"
+wheel: <
+  name: "infra/python/wheels/pyyaml-py3"
+  version: "version:5.3.1"
+>

tools/fuchsia/python/python_binary.gni

@@ -66,6 +66,12 @@ template("python_binary") {
     walk_keys = [ "library_info_barrier" ]
   }
 
+  _vpy_env_target = "${target_name}_vpy_env"
+  copy(_vpy_env_target) {
+    sources = [ "vpython3.txt" ]
+    outputs = [ "$target_out_dir/.vpython3" ]
+  }
+
   # action(target_name) {
   python3_action(target_name) {
     forward_variables_from(invoker,
@@ -79,7 +85,10 @@ template("python_binary") {
       sources += invoker.sources
     }
     inputs = [ _library_infos_json ]
-    deps = [ ":${_library_infos_target}" ]
+    deps = [
+      ":${_library_infos_target}",
+      ":${_vpy_env_target}",
+    ]
 
     # Output must be a .pyz, so our build knows to use a vendored Python
     # interpreter to run them.