Port type checking from mypy to ty

.github/PULL_REQUEST_TEMPLATE.md

@@ -31,5 +31,5 @@ See [CONTRIBUTING.md](https://github.com/Azure-Samples/rag-postgres-openai-pytho
 - [ ] The current tests all pass (`python -m pytest`).
 - [ ] I added tests that prove my fix is effective or that my feature works
 - [ ] I ran `python -m pytest --cov` to verify 100% coverage of added lines
-- [ ] I ran `python -m mypy` to check for type errors
+- [ ] I ran `python -m ty check` to check for type errors
 - [ ] I either used the pre-commit hooks or ran `ruff` manually on my code.

.github/copilot-instructions.md

@@ -98,11 +98,9 @@ Use "Frontend & Backend" configuration in the VS Code Run & Debug menu.
 ```bash
 ruff check .          # Lint code (takes <1 second)
 ruff format .          # Format code (takes <1 second)
-mypy . --python-version 3.12  # Type check (takes ~42 seconds)
+ty check . --python-version 3.12  # Type check
 ```
 
-**NOTE**: MyPy may show 1 minor import error in `evals/safety_evaluation.py` which is expected and safe to ignore.
-
 ### Testing (NEVER CANCEL - full test suite takes ~25 seconds)
 ```bash
 pytest -s -vv --cov --cov-fail-under=85
@@ -123,7 +121,7 @@ pytest tests/e2e.py --tracing=retain-on-failure
 - **Dependencies install**: 90 seconds (use 180+ second timeout)
 - **Frontend npm install**: 22 seconds (use 60+ second timeout)
 - **Frontend build**: 12 seconds (use 30+ second timeout)
-- **MyPy type checking**: 42 seconds (use 90+ second timeout)
+- **ty type checking**: use 90+ second timeout
 - **Full test suite**: 25 seconds (use 60+ second timeout)
 - **Playwright E2E tests**: 2+ minutes (use 300+ second timeout)
 
@@ -138,7 +136,7 @@ pytest tests/e2e.py --tracing=retain-on-failure
 
 2. **Type check (if Python changes)**:
    ```bash
-   mypy . --python-version 3.12
+   ty check . --python-version 3.12
    ```
 
 3. **Run relevant tests**:
@@ -194,7 +192,7 @@ pytest tests/e2e.py --tracing=retain-on-failure
 - `main.bicep` - Main infrastructure definition
 
 ### Configuration Files
-- `pyproject.toml` - Python project config (ruff, mypy, pytest)
+- `pyproject.toml` - Python project config (ruff, ty, pytest)
 - `requirements-dev.txt` - Development dependencies
 - `azure.yaml` - Azure Developer CLI configuration
 - `.env.sample` - Environment variable template
@@ -248,7 +246,7 @@ The GitHub Actions require:
 - Python 3.10+ with specific versions (3.10, 3.11, 3.12)
 - PostgreSQL with pgvector extension
 - Node.js 18+
-- All code passes `ruff check`, `ruff format --check`, and `mypy`
+- All code passes `ruff check`, `ruff format --check`, and `ty check`
 
 ## Load Testing
 

.github/workflows/app-tests.yaml

@@ -114,14 +114,8 @@ jobs:
             npm install
             npm run build
 
-        - name: Setup mypy cache
-          uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
-          with:
-            path: ./.mypy_cache
-            key: mypy${{ matrix.os }}-${{ matrix.python_version }}-${{ hashFiles('requirements-dev.txt', 'src/backend/requirements.txt', 'src/backend/pyproject.toml') }}
-
-        - name: Run MyPy
-          run: python3 -m mypy . --python-version ${{ matrix.python_version }}
+        - name: Run ty
+          run: python3 -m ty check . --python-version ${{ matrix.python_version }} --output-format github
 
         - name: Run Pytest
           run: python3 -m pytest -s -vv --cov --cov-fail-under=85

.gitignore

@@ -128,11 +128,6 @@ venv.bak/
 # mkdocs documentation
 /site
 
-# mypy
-.mypy_cache/
-.dmypy.json
-dmypy.json
-
 # Pyre type checker
 .pyre/
 

.vscode/settings.json

@@ -34,7 +34,6 @@
         ".pytest_cache": true,
         "__pycache__": true,
         "htmlcov": true,
-        ".mypy_cache": true,
         ".coverage": true
     },
     "python-envs.defaultEnvManager": "ms-python.python:system"

evals/generate_ground_truth.py

@@ -121,7 +121,7 @@ def generate_ground_truth_data(num_questions_total: int, num_questions_per_sourc
                 {"role": "system", "content": generate_prompt},
                 {"role": "user", "content": json.dumps(source)},
             ],
-            tools=[qa_pairs_tool(num_questions=2)],  # type: ignore[list-item]
+            tools=[qa_pairs_tool(num_questions=2)],  # ty: ignore[invalid-argument-type]
             max_output_tokens=1000,
             store=False,
         )

pyproject.toml

@@ -5,22 +5,22 @@ lint.select = ["E", "F", "I", "UP"]
 lint.ignore = ["D203"]
 lint.isort.known-first-party = ["fastapi_app"]
 
-[tool.mypy]
-check_untyped_defs = true
-exclude = [".venv/*"]
+[tool.ty.environment]
+root = ["./src/backend", "."]
+
+[tool.ty.analysis]
+allowed-unresolved-imports = [
+    "azure.ai.evaluation.**",
+    "rich.**",
+    "pgvector.**",
+    "evaltools.**",
+]
 
 [tool.pytest.ini_options]
 addopts = "-ra"
 testpaths = ["tests"]
 pythonpath = ['src/backend']
 filterwarnings = ["ignore::DeprecationWarning"]
 
-[[tool.mypy.overrides]]
-module = [
-    "pgvector.*",
-    "evaltools.*"
-]
-ignore_missing_imports = true
-
 [tool.coverage.report]
 show_missing = true

requirements-dev.txt

@@ -1,6 +1,6 @@
 -r src/backend/requirements.txt
 ruff
-mypy
+ty
 types-requests
 pre-commit
 pip-tools

src/backend/fastapi_app/rag_advanced.py

@@ -7,6 +7,7 @@
     ItemHelpers,
     ModelSettings,
     OpenAIResponsesModel,
+    RawResponsesStreamEvent,
     Runner,
     ToolCallOutputItem,
     function_tool,
@@ -198,6 +199,6 @@ async def answer_stream(
         )
 
         async for event in run_results.stream_events():
-            if event.type == "raw_response_event" and isinstance(event.data, ResponseTextDeltaEvent):
+            if isinstance(event, RawResponsesStreamEvent) and isinstance(event.data, ResponseTextDeltaEvent):
                 yield RetrievalResponseDelta(type="response.output_text.delta", delta=str(event.data.delta))
         return

src/backend/fastapi_app/rag_simple.py

@@ -1,7 +1,15 @@
 from collections.abc import AsyncGenerator
 from typing import Optional
 
-from agents import Agent, ItemHelpers, ModelSettings, OpenAIResponsesModel, Runner, set_tracing_disabled
+from agents import (
+    Agent,
+    ItemHelpers,
+    ModelSettings,
+    OpenAIResponsesModel,
+    RawResponsesStreamEvent,
+    Runner,
+    set_tracing_disabled,
+)
 from openai import AsyncOpenAI
 from openai.types.responses import ResponseInputItemParam, ResponseTextDeltaEvent
 
@@ -131,6 +139,6 @@ async def answer_stream(
         )
 
         async for event in run_results.stream_events():
-            if event.type == "raw_response_event" and isinstance(event.data, ResponseTextDeltaEvent):
+            if isinstance(event, RawResponsesStreamEvent) and isinstance(event.data, ResponseTextDeltaEvent):
                 yield RetrievalResponseDelta(type="response.output_text.delta", delta=str(event.data.delta))
         return