Migrate from mypy to ty for type checking (#252)

* Migrate from mypy to ty for type checking

- Replace mypy with ty (Astral's new type checker)
- Update all configuration files (pyproject.toml, setup.cfg)
- Update GitHub Actions workflow to use uvx ty check
- Update AGENT.md, Makefile, and dev.py with new command
- Remove mypy and types-setuptools from requirements-dev.in
- Fix type errors detected by ty (remove unused imports, add type ignore comments for intentional monkey patching)
- All 153 tests pass
- Ty type checking passes with no errors

Amp-Thread-ID: https://ampcode.com/threads/T-3de57a05-de3a-47f2-a4f0-bc95e78d8d13
Co-authored-by: Amp <amp@ampcode.com>

* Fix ty typecheck in CI by using venv

Ty needs to find installed packages in a virtual environment.
Create a venv and activate it before running ty check.

* Replace mypy with ty in lint.yml workflow

Update the lint workflow to use ty instead of mypy for type checking.
Verified locally:
- ✅ ruff check passed
- ✅ ty check passed
- ✅ all 153 tests passed

---------

Co-authored-by: Amp <amp@ampcode.com>

Author: vinitkumar

.github/workflows/lint.yml

@@ -27,8 +27,8 @@ jobs:
           ruff check tests
 
 
-  mypy:
-    name: mypy
+  typecheck:
+    name: ty typecheck
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
@@ -37,11 +37,15 @@ jobs:
         uses: actions/setup-python@v5.2.0
         with:
           python-version: '3.13'
-          cache: 'pip'
-      - run: pip install --upgrade mypy types-requests types-urllib3
-      - name: mypy
-        uses: liskin/gh-problem-matcher-wrap@v2
+      - name: Install uv
+        uses: astral-sh/setup-uv@v6
         with:
-          linters: mypy
-          run: |
-            mypy json2xml
+          enable-cache: true
+      - name: Install dependencies
+        run: |
+          uv venv
+          uv pip install -e .
+      - name: Run ty
+        run: |
+          source .venv/bin/activate
+          uvx ty check json2xml tests

.github/workflows/pythonpackage.yml

@@ -142,9 +142,11 @@ jobs:
 
     - name: Install dependencies
       run: |
-        uv pip install --system -e .
-        uv pip install --system mypy>=1.0.0 types-setuptools
+        uv venv
+        uv pip install -e .
 
-    - name: Run mypy
-      run: mypy json2xml tests
+    - name: Run ty
+      run: |
+        source .venv/bin/activate
+        uvx ty check json2xml tests
 

AGENT.md

@@ -4,7 +4,7 @@
 - Test: `pytest -vv` (all tests) or `pytest tests/test_<name>.py -vv` (single test file)
 - Test with coverage: `pytest --cov=json2xml --cov-report=xml:coverage/reports/coverage.xml --cov-report=term -xvs`
 - Lint: `ruff check json2xml tests`
-- Type check: `mypy json2xml tests`
+- Type check: `uvx ty check json2xml tests`
 - Test all Python versions: `tox`
 - Clean artifacts: `make clean`
 

Makefile

@@ -56,8 +56,8 @@ lint: ## check style with ruff
 lint-fix: ## automatically fix ruff issues
 	ruff check --fix json2xml tests
 
-typecheck: ## check types with mypy
-	mypy json2xml tests
+typecheck: ## check types with ty
+	uvx ty check json2xml tests
 
 test: ## run tests quickly with the default Python
 	pytest --cov=json2xml --cov-report=xml:coverage/reports/coverage.xml --cov-report=term -xvs tests -n auto

dev.py

@@ -37,7 +37,7 @@ def main() -> None:
         ], "Tests")
 
     if command in ("typecheck", "all"):
-        success &= run_command(["mypy", "json2xml", "tests"], "Type checking")
+        success &= run_command(["uvx", "ty", "check", "json2xml", "tests"], "Type checking")
 
     if command == "help":
         print("Usage: python dev.py [command]")

pyproject.toml

@@ -72,3 +72,6 @@ lint.select = [
     "F",
     "W",
 ]
+
+[tool.ty]
+# Type checking configuration with ty

requirements-dev.in

@@ -7,5 +7,4 @@ pytest-xdist==3.8.0
 coverage==7.10.3
 ruff==0.12.8
 setuptools==80.9.0
-mypy==1.17.1
-types-setuptools==80.9.0.20250809
+# Note: ty is run via uvx, not installed as a dependency

requirements-dev.txt

@@ -1,10 +1,6 @@
-#
-# This file is autogenerated by pip-compile with Python 3.13
-# by the following command:
-#
-#    pip-compile requirements-dev.in
-#
-coverage[toml]==7.10.3
+# This file was autogenerated by uv via the following command:
+#    uv pip compile requirements-dev.in -o requirements-dev.txt
+coverage==7.10.3
     # via
     #   -r requirements-dev.in
     #   pytest-cov
@@ -14,14 +10,8 @@ execnet==2.1.1
     # via pytest-xdist
 iniconfig==2.0.0
     # via pytest
-mypy==1.17.1
-    # via -r requirements-dev.in
-mypy-extensions==1.0.0
-    # via mypy
 packaging==24.2
     # via pytest
-pathspec==0.12.1
-    # via mypy
 pluggy==1.5.0
     # via
     #   pytest
@@ -39,14 +29,9 @@ pytest-xdist==3.8.0
     # via -r requirements-dev.in
 ruff==0.12.8
     # via -r requirements-dev.in
-types-setuptools==80.9.0.20250809
+setuptools==80.9.0
     # via -r requirements-dev.in
-typing-extensions==4.12.2
-    # via mypy
 urllib3==2.5.0
     # via -r requirements.in
 xmltodict==0.14.2
     # via -r requirements-dev.in
-
-# The following packages are considered to be unsafe in a requirements file:
-# setuptools

setup.cfg

@@ -21,15 +21,8 @@ max-line-length=120
 [aliases]
 # Define setup.py command aliases here
 
-[mypy]
-check_untyped_defs = true
-disallow_any_generics = true
-disallow_incomplete_defs = true
-disallow_untyped_defs = true
-no_implicit_optional = true
-warn_redundant_casts = true
-warn_unused_ignores = true
-ignore_missing_imports = true
+[tool.ty]
+# Ty configuration is now in pyproject.toml
 
 
 [coverage:run]

tests/test_dict2xml.py

@@ -11,7 +11,6 @@
     from _pytest.fixtures import FixtureRequest
     from _pytest.logging import LogCaptureFixture
     from _pytest.monkeypatch import MonkeyPatch
-    from pytest_mock.plugin import MockerFixture
 
 
 class TestDict2xml:
@@ -808,8 +807,8 @@ def patched_get_unique_id(element: str) -> str:
                     this_id = module.make_id(element)  # This exercises line 52
             return ids[-1]
 
-        module.make_id = mock_make_id
-        module.get_unique_id = patched_get_unique_id
+        module.make_id = mock_make_id  # type: ignore[assignment]
+        module.get_unique_id = patched_get_unique_id  # type: ignore[assignment]
 
         try:
             result = dicttoxml.get_unique_id("test")
@@ -1025,7 +1024,7 @@ def mock_is_primitive(val: Any) -> bool:
                 return True
             return original_is_primitive(val)
 
-        module.is_primitive_type = mock_is_primitive
+        module.is_primitive_type = mock_is_primitive  # type: ignore[assignment]
         try:
             item = {"@val": {"test": "data"}}
             result = dicttoxml.dict2xml_str(