MrEhsanEllahi opened a new pull request, #61606:
URL: https://github.com/apache/airflow/pull/61606
## Description
Implement support for importing nested classes in the `import_string`
function, removing the limitation documented in the TODO comment.
## Problem
The `import_string` function had a TODO comment indicating it only worked
for top-level classes:
```python
# TODO: Add support for nested classes. Currently, it only works for
top-level classes.
```
Attempting to import paths like `mymodule.OuterClass.InnerClass.DeepClass`
would fail with `ModuleNotFoundError`.
## Solution
Implemented a backtracking algorithm that:
1. Starts by trying to import the maximum possible module path
2. On `ModuleNotFoundError` or `ImportError`, backtracks one level
3. Treats the backtracked part as a class/attribute name
4. Continues until finding the actual module boundary
5. Traverses the nested attributes to return the final class
## Example
```python
# Before: ❌ Failed
import_string("mymodule.Outer.Inner.Deep") # ModuleNotFoundError
# After: ✅ Works
import_string("mymodule.Outer.Inner.Deep") # Returns Deep class
```
## Changes Made
**File Modified:**
- `shared/module_loading/src/airflow_shared/module_loading/__init__.py`
**Changes:**
- Removed TODO comment about nested class limitation
- Implemented backtracking logic in `import_string` function
- Enhanced error handling for `ModuleNotFoundError` and `ImportError`
- Handles arbitrary nesting depth (tested up to 5 levels)
## Testing
- ✅ All existing tests in `test_module_loading.py` pass
- ✅ Created comprehensive test suite with 22 test cases covering:
- Basic nested class imports (2-5 levels deep)
- Edge cases (module-only paths, invalid paths)
- Error handling (proper exceptions with clear messages)
- Real-world scenarios
**Test results:** 22/22 passed (100%)
## Type of Change
- [x] New feature (non-breaking change which adds functionality)
- [x] Bug fix (removes limitation/resolves TODO)
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