[python] Fix enum member names corrupted by YAML 1.1/1.2 boundary

.chronus/changes/http-client-python-non-string-description-2026-7-2.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Fix enum member names derived from date-like TypeSpec labels (e.g. `` `2020-01-01` ``) being corrupted by the js-yaml (YAML 1.2) to PyYAML (YAML 1.1) boundary. String scalars are now force-quoted when serializing the code model so names such as `2020_01_01` round-trip as strings instead of being read back as integers

packages/http-client-python/emitter/src/emitter.ts

@@ -1,6 +1,5 @@
 import { createSdkContext } from "@azure-tools/typespec-client-generator-core";
 import { EmitContext, emitFile, joinPaths, NoTarget } from "@typespec/compiler";
-import jsyaml from "js-yaml";
 import pkgJson from "../../package.json" with { type: "json" };
 import { emitCodeModel } from "./code-model.js";
 import {
@@ -9,6 +8,7 @@ import {
   PYGEN_WHEEL_FILENAME,
   PYODIDE_VERSION,
 } from "./constants.js";
+import { dumpCodeModelToYaml } from "./external-process.js";
 import { PythonEmitterOptions, PythonSdkContext, reportDiagnostic } from "./lib.js";
 import { runNodeEmit } from "./node-runner.js";
 import { loadPyodide, PyodideInterface } from "./pyodide-loader.js";
@@ -250,7 +250,7 @@ async function onEmitMain(context: EmitContext<PythonEmitterOptions>) {
     pyodide.FS.mkdirTree("/yaml");
     pyodide.FS.mkdirTree("/output");
     clearMemfsDirectory(pyodide, "/output");
-    pyodide.FS.writeFile(yamlFilePath, jsyaml.dump(parsedYamlMap));
+    pyodide.FS.writeFile(yamlFilePath, dumpCodeModelToYaml(parsedYamlMap));
 
     await runPyodideGeneration(pyodide, "/output", yamlFilePath, commandArgs);
     await copyPyodideOutputToHost(context, pyodide, "/output");

packages/http-client-python/emitter/src/external-process.ts

@@ -11,6 +11,23 @@ export function createTempPath(extension: string, prefix: string = "") {
   return joinPaths(tspCodeGenTempDir, prefix + randomUUID() + extension);
 }
 
+/**
+ * Serialize the given codemodel to a YAML string.
+ *
+ * The generated YAML is consumed by the Python generator, which parses it with
+ * PyYAML (YAML 1.1). js-yaml, on the other hand, dumps using YAML 1.2 rules, so
+ * plain scalars such as `2020_01_01` (a snake-cased enum member name) are left
+ * unquoted because YAML 1.2 does not treat underscores as integer separators.
+ * PyYAML would then read `2020_01_01` back as the integer `20200101`, corrupting
+ * string values (e.g. enum member names, descriptions). Forcing every string
+ * scalar to be quoted guarantees that PyYAML round-trips them as strings.
+ * @param codemodel Codemodel to serialize
+ * @return the YAML representation of the codemodel.
+ */
+export function dumpCodeModelToYaml(codemodel: unknown): string {
+  return jsyaml.dump(codemodel, { forceQuotes: true, quotingType: '"' });
+}
+
 /**
  * Save the given codemodel in a yaml file.
  * @param name Name of the codemodel. To give a guide to the temp file name.
@@ -20,7 +37,7 @@ export function createTempPath(extension: string, prefix: string = "") {
 export async function saveCodeModelAsYaml(name: string, codemodel: unknown): Promise<string> {
   await mkdir(tspCodeGenTempDir, { recursive: true });
   const filename = createTempPath(".yaml", name);
-  const yamlStr = jsyaml.dump(codemodel);
+  const yamlStr = dumpCodeModelToYaml(codemodel);
   await writeFile(filename, yamlStr);
   return filename;
 }

packages/http-client-python/emitter/test/external-process.test.ts

@@ -0,0 +1,28 @@
+import { ok, strictEqual } from "assert";
+import { load } from "js-yaml";
+import { describe, it } from "vitest";
+import { dumpCodeModelToYaml } from "../src/external-process.js";
+
+describe("typespec-python: external-process", () => {
+  // The Python generator parses the emitted YAML with PyYAML (YAML 1.1), where a plain
+  // scalar such as `2020_01_01` is interpreted as the integer `20200101`. js-yaml dumps
+  // using YAML 1.2 rules and would otherwise leave such string scalars unquoted, so we
+  // must force-quote strings to keep enum member names (and other string values) intact.
+  it("force-quotes string scalars that YAML 1.1 would misinterpret", () => {
+    const yaml = dumpCodeModelToYaml({ name: "2020_01_01" });
+    // The scalar must be quoted, otherwise PyYAML reads it back as the integer 20200101.
+    ok(yaml.includes('"2020_01_01"'), `expected the underscore scalar to be quoted, got: ${yaml}`);
+    ok(
+      !/name:\s*2020_01_01\s*$/m.test(yaml),
+      `expected no unquoted underscore scalar, got: ${yaml}`,
+    );
+  });
+
+  it("keeps string values as strings after a round-trip", () => {
+    const codeModel = { name: "2020_01_01", value: "2020-01-01", plain: "hello" };
+    const roundTripped = load(dumpCodeModelToYaml(codeModel)) as Record<string, unknown>;
+    strictEqual(roundTripped.name, "2020_01_01");
+    strictEqual(roundTripped.value, "2020-01-01");
+    strictEqual(roundTripped.plain, "hello");
+  });
+});