fix(lambda-python): handler path is incorrectly generated when using …

…PythonFunction (#20083)

When using PythonFunction, current implementation generates `handler` value incorrectly.

## Code

```typescript
new PythonFunction(stack, 'handler', {
    entry: 'test/lambda-handler-sub-nested',
    index: 'inner/inner2/custom_index.py',
    handler: 'custom_handler',
    runtime: Runtime.PYTHON_3_8,
});
```

## Expected

```yaml
Handler: inner.inner2.custom_index.custom_handler
```

## Current Behaviour

```yaml
Handler: inner.inner2/custom_index.custom_handler
```

This PR fix the issue by modifying string replace pattern.

----

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### New Features

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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-lambda-python/lib/function.ts

@@ -68,7 +68,7 @@ export class PythonFunction extends Function {
       throw new Error(`Cannot find index file at ${resolvedIndex}`);
     }
 
-    const resolvedHandler =`${index.slice(0, -3)}.${handler}`.replace('/', '.');
+    const resolvedHandler =`${index.slice(0, -3)}.${handler}`.replace(/\//g, '.');
 
     if (props.runtime && props.runtime.family !== RuntimeFamily.PYTHON) {
       throw new Error('Only `PYTHON` runtimes are supported.');

packages/@aws-cdk/aws-lambda-python/test/function.test.ts

@@ -77,6 +77,23 @@ test('PythonFunction with index in a subdirectory', () => {
   });
 });
 
+test('PythonFunction with index in a nested subdirectory', () => {
+  new PythonFunction(stack, 'handler', {
+    entry: 'test/lambda-handler-sub-nested',
+    index: 'inner/inner2/custom_index.py',
+    handler: 'custom_handler',
+    runtime: Runtime.PYTHON_3_8,
+  });
+
+  expect(Bundling.bundle).toHaveBeenCalledWith(expect.objectContaining({
+    entry: expect.stringMatching(/aws-lambda-python\/test\/lambda-handler-sub-nested$/),
+  }));
+
+  Template.fromStack(stack).hasResourceProperties('AWS::Lambda::Function', {
+    Handler: 'inner.inner2.custom_index.custom_handler',
+  });
+});
+
 test('throws when index is not py', () => {
   expect(() => new PythonFunction(stack, 'Fn', {
     entry: 'test/lambda-handler',

packages/@aws-cdk/aws-lambda-python/test/lambda-handler-sub-nested/inner/inner2/custom_index.py

@@ -0,0 +1,5 @@
+from http import HTTPStatus
+
+def handler(event, context):
+  print('No dependencies')
+  return HTTPStatus.OK.value