[python] Add discontinue date for Python 3.6 (#7709)

This PR does a few things:
- Changes the existing warning message for Python 3.6 to print a discontinue date
- Will automatically fail new Python 3.6 deployments created after that date
- Consolidates logic to make Python version selection work in a similar manner to Node.js version selection
- Changes tests from JS to TS

packages/python/test/integration.test.ts

@@ -0,0 +1,94 @@
+const fs = require('fs');
+const path = require('path');
+const assert = require('assert');
+const fetch = require('node-fetch');
+const execa = require('execa');
+const { spawn } = require('child_process');
+
+const {
+  packAndDeploy,
+  testDeployment,
+} = require('../../../test/lib/deployment/test-deployment.js');
+
+jest.setTimeout(4 * 60 * 1000);
+const buildUtilsUrl = '@canary';
+let builderUrl: string;
+
+beforeAll(async () => {
+  const builderPath = path.resolve(__dirname, '..');
+  builderUrl = await packAndDeploy(builderPath);
+  console.log('builderUrl', builderUrl);
+});
+
+const fixturesPath = path.resolve(__dirname, 'fixtures');
+
+it('should match the probes against Python dev servers', async () => {
+  const fixture = path.join(fixturesPath, '00-request-path');
+
+  await execa(
+    'pip3',
+    ['install', '--user', '--upgrade', 'setuptools', 'wheel'],
+    {
+      cwd: fixture,
+      stdio: 'inherit',
+    }
+  );
+  await execa('pip3', ['install', '--user', '-r', 'requirements.txt'], {
+    cwd: fixture,
+    stdio: 'inherit',
+  });
+
+  const ports = new Map();
+  ports.set('/api/python.py', 8001);
+  ports.set('/api/wsgi.py', 8002);
+  ports.set('/api/asgi.py', 8003);
+
+  const { probes } = require(path.join(fixture, 'vercel.json'));
+
+  const pythonServer = spawn('python3', ['api/python.py'], {
+    cwd: fixture,
+    stdio: 'inherit',
+  });
+
+  const wsgiServer = spawn('python3', ['api/wsgi.py'], {
+    cwd: fixture,
+    stdio: 'inherit',
+  });
+
+  const asgiServer = spawn('python3', ['api/asgi.py'], {
+    cwd: fixture,
+    stdio: 'inherit',
+  });
+
+  try {
+    // wait a few seconds for the dev servers to boot-up
+    await new Promise(r => setTimeout(r, 3000));
+
+    for (const { path, mustContain } of probes) {
+      const port = ports.get(path.substring(0, path.indexOf('?')));
+      const res = await fetch(`http://localhost:${port}${path}`);
+      const body = await res.text();
+      assert(
+        body.includes(mustContain),
+        `Expected to contain "${mustContain}" but got "${body}"`
+      );
+    }
+  } finally {
+    process.kill(pythonServer.pid);
+    process.kill(wsgiServer.pid);
+    process.kill(asgiServer.pid);
+  }
+});
+
+// eslint-disable-next-line no-restricted-syntax
+for (const fixture of fs.readdirSync(fixturesPath)) {
+  // eslint-disable-next-line no-loop-func
+  it(`should build ${fixture}`, async () => {
+    await expect(
+      testDeployment(
+        { builderUrl, buildUtilsUrl },
+        path.join(fixturesPath, fixture)
+      )
+    ).resolves.toBeDefined();
+  });
+}