Check type issues with ty and fix problems it finds (#100)

* Check type issues with ty and fix problems it finds

Adds ty to the dev dependency group and clears every diagnostic it
surfaces against the `us` package:

- Drop unused `# type: ignore` directives on jellyfish and pytest.
- Restructure `lookup()` so `fallback_key` is only ever bound to a
  `str`, removing the false `None | str` dict-key write.
- Guard `state.shapefile_urls()` against `None` in the CLI and in the
  skipped network test before iterating.
- Narrow `state.fips` with an assert in `test_county_fips_prefixed_by_state`.
- Suppress the `requests` import inside the permanently-skipped
  `test_head` with `# ty: ignore[unresolved-import]`.

Author: jcarbaugh

.github/workflows/pythonpackage.yml

@@ -25,6 +25,9 @@ jobs:
       - name: Check code format with Ruff
         run: uv run ruff format --check us
 
+      - name: Check types with ty
+        run: uv run ty check us
+
   testing:
     needs: linting
     runs-on: ubuntu-latest

pyproject.toml

@@ -29,7 +29,12 @@ dependencies = ['jellyfish']
 states = "us.cli.states:main"
 
 [dependency-groups]
-dev = ['ruff', 'pytest', 'pytz']
+dev = [
+    'ruff',
+    'pytest',
+    'pytz',
+    "ty>=0.0.38",
+]
 
 [tool.ruff]
 line-length = 120

us/cli/states.py

@@ -38,8 +38,10 @@ def main():
 
         sys.stdout.write("\n")
         sys.stdout.write("  shapefiles:\n")
-        for region, url in state.shapefile_urls().items():
-            sys.stdout.write("    %s: %s\n" % (region, url))
+        urls = state.shapefile_urls()
+        if urls is not None:
+            for region, url in urls.items():
+                sys.stdout.write("    %s: %s\n" % (region, url))
 
         sys.stdout.write("\n")
 

us/states.py

@@ -4,7 +4,7 @@
 from typing import Any, Callable, Dict, Iterable, List, Optional, Type
 from urllib.parse import urljoin
 
-import jellyfish  # type: ignore
+import jellyfish
 
 FIPS_RE = re.compile(r"^\d{2}$")
 ABBR_RE = re.compile(r"^[a-zA-Z]{2}$")
@@ -137,7 +137,6 @@ def lookup(
     # fallback results are cached under a separate, fallback-specific key so
     # they never leak into non-fallback lookups -- or lookups using a
     # different fallback -- of the same value
-    fallback_key = None
     if fallback_func is not None:
         fallback_key = f"{cache_key}:fallback:{fallback_func!r}"
         if use_cache and fallback_key in _lookup_cache:

us/tests/test_us.py

@@ -1,8 +1,8 @@
 import re
 from itertools import chain
 
-import jellyfish  # type: ignore
-import pytest  # type: ignore
+import jellyfish
+import pytest
 import pytz
 
 import us
@@ -251,10 +251,15 @@ def test_dc():
 
 @pytest.mark.skip
 def test_head():
-    import requests
+    # `requests` is intentionally not declared as a dependency; this test
+    # is permanently skipped and the import is dead code for ty.
+    import requests  # ty: ignore[unresolved-import]
 
     for state in us.STATES_AND_TERRITORIES:
-        for url in state.shapefile_urls().values():
+        urls = state.shapefile_urls()
+        if urls is None:
+            continue
+        for url in urls.values():
             resp = requests.head(url)
             assert resp.status_code == 200
 
@@ -312,6 +317,7 @@ def test_county_fips_format():
 
 def test_county_fips_prefixed_by_state():
     for state in us.STATES_AND_TERRITORIES:
+        assert state.fips is not None, f"{state.abbr}: missing state fips"
         for county in state.counties:
             assert county.fips.startswith(state.fips), (
                 f"{state.abbr}: county {county.name} fips {county.fips} not prefixed by state fips {state.fips}"