[codegen/python] Fix relative import path (#4796)

pkg/codegen/python/gen.go

@@ -115,17 +115,32 @@ func (mod *modContext) genHeader(w io.Writer, needsSDK bool) {
 		rel, err := filepath.Rel(mod.mod, "")
 		contract.Assert(err == nil)
 		relRoot := path.Dir(rel)
+		relImport := relPathToRelImport(relRoot)
 
 		fmt.Fprintf(w, "import json\n")
 		fmt.Fprintf(w, "import warnings\n")
 		fmt.Fprintf(w, "import pulumi\n")
 		fmt.Fprintf(w, "import pulumi.runtime\n")
 		fmt.Fprintf(w, "from typing import Union\n")
-		fmt.Fprintf(w, "from %s import utilities, tables\n", relRoot)
+		fmt.Fprintf(w, "from %s import utilities, tables\n", relImport)
 		fmt.Fprintf(w, "\n")
 	}
 }
 
+func relPathToRelImport(relPath string) string {
+	// Convert relative path to relative import e.g. "../.." -> "..."
+	// https://realpython.com/absolute-vs-relative-python-imports/#relative-imports
+	relImport := "."
+	for _, component := range strings.Split(relPath, "/") {
+		if component == ".." {
+			relImport += "."
+		} else {
+			relImport += component
+		}
+	}
+	return relImport
+}
+
 type fs map[string][]byte
 
 func (fs fs) add(path string, contents []byte) {

pkg/codegen/python/gen_test.go

@@ -0,0 +1,27 @@
+package python
+
+import "testing"
+
+var pathTests = []struct {
+	input    string
+	expected string
+}{
+	{"", "."},
+	{"../", ".."},
+	{"../..", "..."},
+	{"../../..", "...."},
+	{"something", ".something"},
+	{"../parent", "..parent"},
+	{"../../module", "...module"},
+}
+
+func TestRelPathToRelImport(t *testing.T) {
+	for _, tt := range pathTests {
+		t.Run(tt.input, func(t *testing.T) {
+			result := relPathToRelImport(tt.input)
+			if result != tt.expected {
+				t.Errorf("expected \"%s\"; got \"%s\"", tt.expected, result)
+			}
+		})
+	}
+}