Improve the type annotation of empty container initializations (#1447)

nathanjmcdougall · web-flow · commit b4d168ea427c · 2026-03-22T16:42:32.000+13:00
* Improve the type annotation of empty container initializations This mostly comes up when using the accumulator pattern. Toward #1332 * Revert difficult change (to placate `ty`) Also clarify the importance of static checks in the `usethis-qa-static-checks` skill
diff --git a/.agents/skills/usethis-qa-static-checks/SKILL.md b/.agents/skills/usethis-qa-static-checks/SKILL.md
@@ -4,7 +4,7 @@ description: Perform static code checks
 compatibility: usethis, Python, prek, basedpyright
 license: MIT
 metadata:
-  version: "1.1"
+  version: "1.2
 ---
 
 # Static Checks
@@ -15,3 +15,9 @@ To perform static checks on the codebase, run:
 uv run prek run -a
 uv run basedpyright
 ```
+
+Note that we are interested in both errors and warnings from these tools - we should always fix both.
+
+## When to run these checks:
+
+Before submitting changes for review, **always** run these static checks. This should be done every time, even for small changes, to avoid slowing down the code review process unnecessarily.
diff --git a/src/usethis/_backend/uv/deps.py b/src/usethis/_backend/uv/deps.py
@@ -47,6 +47,6 @@ def get_default_groups_via_uv() -> list[str]:
                 PyprojectTOMLManager()[["tool", "uv", "default-groups"]]
             )
     except (KeyError, ValidationError):
-        default_groups = []
+        default_groups: list[str] = []
 
     return default_groups
diff --git a/src/usethis/_backend/uv/python.py b/src/usethis/_backend/uv/python.py
@@ -26,7 +26,7 @@ def get_supported_uv_minor_python_versions() -> list[PythonVersion]:
     except (MissingRequiresPythonError, PyprojectTOMLNotFoundError):
         return [PythonVersion.from_interpreter()]
 
-    versions = set()
+    versions: set[str] = set()
     for version in get_available_uv_python_versions():
         # N.B. a standard range won't include alpha versions.
         if requires_python.contains(version):
diff --git a/src/usethis/_core/status.py b/src/usethis/_core/status.py
@@ -25,7 +25,7 @@ def use_development_status(
             mgr[["project", "classifiers"]]
         )
     except (KeyError, ValidationError):
-        existing_classifiers = []
+        existing_classifiers: list[str] = []
     existing_status_classifiers = {
         classifier
         for classifier in existing_classifiers
diff --git a/src/usethis/_deps.py b/src/usethis/_deps.py
@@ -120,7 +120,7 @@ def register_default_group(group: str) -> None:
     default_groups = get_default_groups()
 
     # Choose which groups we want to add
-    groups_to_add = []
+    groups_to_add: list[str] = []
     if group not in default_groups:
         groups_to_add.append(group)
         # Add "dev" if section is empty or if we're adding a new group and "dev" isn't present
diff --git a/src/usethis/_file/ini/io_.py b/src/usethis/_file/ini/io_.py
@@ -356,7 +356,7 @@ def __delitem__(self, keys: Sequence[Key]) -> None:
         elif len(keys) == 2:
             (section_key, option_key) = keys
 
-            section_strkeys = []
+            section_strkeys: list[str] = []
             for section_strkey in _itermatches(self.get().sections(), key=section_key):
                 section_strkeys.append(section_strkey)
 
diff --git a/src/usethis/_file/pyproject_toml/requires_python.py b/src/usethis/_file/pyproject_toml/requires_python.py
@@ -77,7 +77,7 @@ def get_required_minor_python_versions() -> list[PythonVersion]:
     # always deal with just major version 3 in practice.
     min_minor_in_spec = min(all_minors)
 
-    supported_versions = []
+    supported_versions: list[PythonVersion] = []
     # Generate all major.minor combinations in range
     # Basically, do a sophisticated brute-force search
     for major in range(min_version[0], max_version[0] + 1):
@@ -101,7 +101,7 @@ def get_required_minor_python_versions() -> list[PythonVersion]:
 
             # Get patch versions mentioned for this major.minor in the specifier
             # The extremes will lie +/- 1 from any named patch version
-            patches_to_check = set()
+            patches_to_check: set[int] = set()
             major_minor_key = (major, minor)
             if major_minor_key in patches_by_short:
                 for patch in patches_by_short[major_minor_key]:
diff --git a/src/usethis/_file/yaml/update.py b/src/usethis/_file/yaml/update.py
@@ -127,11 +127,11 @@ def _shared_id_sequences(*seqs: Sequence[object]) -> Sequence[list[int]]:
     # we can store this information as a list of elements, where the index corresponds
     # to the integer representation.
 
-    iseqs = []
-    rep = []
+    iseqs: list[list[int]] = []
+    rep: list[object] = []
 
     for seq in seqs:
-        iseq = []
+        iseq: list[int] = []
         for element in seq:
             for idx, rep_element in enumerate(rep):
                 if element == rep_element:
diff --git a/src/usethis/_integrations/ci/bitbucket/pipeweld.py b/src/usethis/_integrations/ci/bitbucket/pipeweld.py
@@ -36,7 +36,7 @@ def get_pipeweld_pipeline_from_default(
     default = model.pipelines.default
 
     if default is None:
-        items = []
+        items: list[schema.StepItem | schema.ParallelItem | schema.StageItem] = []
     elif isinstance(default.root, schema.ImportPipeline):
         msg = (
             "Cannot add step to default pipeline in 'bitbucket-pipelines.yml' because "
@@ -117,7 +117,7 @@ def apply_pipeweld_instruction_via_model(
     default = pipelines.default
 
     if default is None:
-        items = []
+        items: list[schema.StepItem | schema.ParallelItem | schema.StageItem] = []
     elif isinstance(default.root, schema.ImportPipeline):
         msg = (
             f"Cannot add step '{step_to_insert.name}' to default pipeline in "
diff --git a/src/usethis/_integrations/ci/bitbucket/steps.py b/src/usethis/_integrations/ci/bitbucket/steps.py
@@ -375,7 +375,7 @@ def _censor_stage_item_step(
 ) -> schema.StageItem | None:
     step1s = item.stage.steps
 
-    new_step1s = []
+    new_step1s: list[schema.Step1] = []
     for step1 in step1s:
         if bitbucket_steps_are_equivalent(step1tostep(step1), step):
             continue
@@ -474,7 +474,7 @@ def _get_steps_in_pipeline(pipeline: schema.Pipeline) -> list[schema.Step]:
 
     items = pipeline.root.root
 
-    steps = []
+    steps: list[schema.Step] = []
     for item in items:
         steps.extend(get_steps_in_pipeline_item(item))
 
diff --git a/src/usethis/_integrations/pre_commit/hooks.py b/src/usethis/_integrations/pre_commit/hooks.py
@@ -114,7 +114,7 @@ def insert_repo(
     # after the last precedent
 
     inserted = False
-    repos = []
+    repos: list[schema.LocalRepo | schema.UriRepo | schema.MetaRepo] = []
 
     if predecessor is None:
         # If there is no predecessor, we can just append the new repo
diff --git a/src/usethis/_integrations/project/imports.py b/src/usethis/_integrations/project/imports.py
@@ -47,7 +47,7 @@ def get_layered_architectures(pkg_name: str) -> dict[str, LayeredArchitecture]:
     """
     graph = _get_graph(pkg_name)
 
-    arch_by_module = {}
+    arch_by_module: dict[str, LayeredArchitecture] = {}
 
     for module in sorted(graph.modules):
         arch = _get_module_layered_architecture(module, graph=graph)
@@ -61,14 +61,14 @@ def _get_module_layered_architecture(
 ) -> LayeredArchitecture:
     deps_by_module = _get_child_dependencies(module, graph=graph)
 
-    layered = set()
-    layers = []
+    layered: set[str] = set()
+    layers: list[set[str]] = []
 
     for _ in range(len(deps_by_module)):
         # Form a layer: cycle through all siblings. For ones with no deps, add them
         # to the layer and ignore them in the next iteration.
 
-        layer = set()
+        layer: set[str] = set()
         for m, deps in deps_by_module.items():
             if m in layered:
                 continue
@@ -83,7 +83,7 @@ def _get_module_layered_architecture(
         layers.append(layer)
         layered.update(layer)
 
-    excluded = set()
+    excluded: set[str] = set()
     for m in deps_by_module:
         if m not in layered:
             excluded.add(m)
@@ -124,7 +124,7 @@ def _get_child_dependencies(
     """
     children = sorted(graph.find_children(module))
 
-    deps_by_module = {}
+    deps_by_module: dict[str, set[str]] = {}
     for child in children:
         downstreams = graph.find_upstream_modules(module=child, as_package=True)
         downstreams = _filter_to_submodule(downstreams, submodule=module)
@@ -135,7 +135,7 @@ def _get_child_dependencies(
 
 
 def _filter_to_submodule(modules: set[str], *, submodule: str) -> set[str]:
-    filtered = set()
+    filtered: set[str] = set()
     for module in modules:
         if module.startswith(submodule + "."):
             filtered.add(_narrow_to_submodule(module, submodule=submodule))
diff --git a/src/usethis/_integrations/pydantic/dump.py b/src/usethis/_integrations/pydantic/dump.py
@@ -72,7 +72,7 @@ def _fancy_model_dump_list(
     if not isinstance(reference, list):
         reference = []
 
-    x = []
+    x: list[ModelRepresentation] = []
     for value, ref in zip_longest(model, reference, fillvalue=_FILL_VALUE):
         if value is _FILL_VALUE:
             # we've exhausted all the content.
@@ -96,7 +96,7 @@ def _fancy_model_dump_dict(
 ) -> ModelRepresentation:
     if order_by_cls is None:
         order_by_cls = {}
-    d = {}
+    d: dict[str, ModelRepresentation] = {}
     for key, value in model.items():
         if reference is None:
             value_ref = None
@@ -122,7 +122,7 @@ def _fancy_model_dump_base_model(
     if order_by_cls is None:
         order_by_cls = {}
 
-    d = {}
+    d: dict[str, ModelRepresentation] = {}
     for key, value in model:
         default_value = model.__class__.model_fields[key].default
 
@@ -158,7 +158,7 @@ def _fancy_model_dump_base_model(
     except KeyError:
         return d
 
-    ordered_d = {}
+    ordered_d: dict[str, ModelRepresentation] = {}
     for key in order:
         if key in d:
             ordered_d[key] = d.pop(key)
diff --git a/src/usethis/_integrations/sonarqube/config.py b/src/usethis/_integrations/sonarqube/config.py
@@ -104,7 +104,7 @@ def _get_sonarqube_exclusions() -> list[str]:
             PyprojectTOMLManager()[["tool", "usethis", "sonarqube", "exclusions"]]
         )
     except (FileNotFoundError, KeyError, ValidationError):
-        exclusions = []
+        exclusions: list[str] = []
     for exclusion in exclusions:
         TypeAdapter(str).validate_python(exclusion)
 
diff --git a/src/usethis/_io.py b/src/usethis/_io.py
@@ -238,7 +238,7 @@ def print_keys(keys: Sequence[Key]) -> str:
         >>> print_keys([re.compile(r"importlinter:contracts:.*")])
         '<REGEX("importlinter:contracts:.*")>'
     """
-    components = []
+    components: list[str] = []
     for key in keys:
         if isinstance(key, str):
             components.append(key)
diff --git a/src/usethis/_pipeweld/func.py b/src/usethis/_pipeweld/func.py
@@ -99,7 +99,7 @@ def _partition_series_component(
         self, component: Series, *, predecessor: str | None
     ) -> tuple[Partition, list[Instruction]]:
         partitions: list[Partition] = []
-        instructions = []
+        instructions: list[Instruction] = []
         for subcomponent in component.root:
             partition, these_instructions = self.partition_component(
                 subcomponent,
@@ -411,7 +411,7 @@ def _parallel_merge_partitions(
         or top_ranked_prerequisite_endpoints
     )
 
-    instructions = []
+    instructions: list[Instruction] = []
     if prerequisite_component is not None:
         new_instructions, _ = _get_instructions_for_insertion(
             prerequisite_component, after=predecessor
@@ -475,7 +475,7 @@ def _get_instructions_for_insertion(
     if isinstance(component, str):
         return [InsertSuccessor(after=after, step=component)], component
     elif isinstance(component, Series):
-        instructions = []
+        instructions: list[Instruction] = []
         for subcomponent in component.root:
             new_instructions, endpoint = _get_instructions_for_insertion(
                 subcomponent, after=after
@@ -589,7 +589,7 @@ def get_endpoint(component: str | Series | DepGroup | Parallel) -> str:
         msg = "No endpoints are defined for a Series with no steps."
         raise ValueError(msg)
     elif isinstance(component, Parallel):
-        endpoints = []
+        endpoints: list[str] = []
         for subcomponent in component.root:
             with contextlib.suppress(ValueError):
                 endpoints.append(get_endpoint(subcomponent))
diff --git a/src/usethis/_tool/base.py b/src/usethis/_tool/base.py
@@ -40,7 +40,7 @@
 if TYPE_CHECKING:
     from collections.abc import Sequence
 
-    from usethis._io import KeyValueFileManager
+    from usethis._io import Key, KeyValueFileManager
     from usethis._tool.config import ConfigItem
     from usethis._tool.rule import Rule
 
@@ -338,7 +338,7 @@ def _add_config_item(
         # using at least a shared subset of those e.g. ["tool", "ruff"], and
         # preferentially add to the highest-priority file manager which already has
         # config at that shared key sequence.
-        shared_keys = []
+        shared_keys: list[Key] = []
         for key in entry.keys:
             shared_keys.append(key)
             new_file_managers = [
diff --git a/src/usethis/_tool/impl/base/deptry.py b/src/usethis/_tool/impl/base/deptry.py
@@ -45,7 +45,7 @@ def ignored_rules(self) -> list[Rule]:
         try:
             rules = TypeAdapter(list[Rule]).validate_python(file_manager[keys])
         except (KeyError, FileNotFoundError, ValidationError):
-            rules = []
+            rules: list[Rule] = []
 
         return rules
 
diff --git a/src/usethis/_tool/impl/base/pytest.py b/src/usethis/_tool/impl/base/pytest.py
@@ -117,7 +117,7 @@ def get_bitbucket_steps(
 
         backend = get_backend()
 
-        steps = []
+        steps: list[bitbucket_schema.Step] = []
         for version in versions:
             if backend is BackendEnum.uv:
                 step = bitbucket_schema.Step(
@@ -154,7 +154,7 @@ def get_bitbucket_steps(
 
     @final
     def get_managed_bitbucket_step_names(self) -> list[str]:
-        names = set()
+        names: set[str] = set()
         for step in get_steps_in_default():
             if step.name is not None:
                 match = re.match(r"^Test on 3\.\d{1,2}$", step.name)
diff --git a/src/usethis/_tool/impl/base/ruff.py b/src/usethis/_tool/impl/base/ruff.py
@@ -105,7 +105,7 @@ def print_how_to_use_formatter(self) -> None:
 
     @final
     def pre_commit_config(self) -> PreCommitConfig:
-        repo_configs = []
+        repo_configs: list[PreCommitRepoConfig] = []
         if self.is_linter_used():
             repo_configs.append(
                 PreCommitRepoConfig(
@@ -139,7 +139,7 @@ def get_bitbucket_steps(
     ) -> list[bitbucket_schema.Step]:
         backend = get_backend()
 
-        steps = []
+        steps: list[bitbucket_schema.Step] = []
         if self.is_linter_used():
             if backend is BackendEnum.uv:
                 steps.append(
@@ -209,7 +209,7 @@ def selected_rules(self) -> list[Rule]:
         try:
             rules = TypeAdapter(list[Rule]).validate_python(file_manager[keys])
         except (KeyError, FileNotFoundError, ValidationError):
-            rules = []
+            rules: list[Rule] = []
 
         return rules
 
@@ -221,7 +221,7 @@ def ignored_rules(self) -> list[Rule]:
         try:
             rules = TypeAdapter(list[Rule]).validate_python(file_manager[keys])
         except (KeyError, FileNotFoundError, ValidationError):
-            rules = []
+            rules: list[Rule] = []
 
         return rules
 
@@ -252,7 +252,7 @@ def get_ignored_rules_in_glob(self, glob: str) -> list[Rule]:
         try:
             rules = TypeAdapter(list[Rule]).validate_python(file_manager[keys])
         except (KeyError, FileNotFoundError, ValidationError):
-            rules = []
+            rules: list[Rule] = []
 
         return rules
 
diff --git a/src/usethis/_tool/impl/spec/import_linter.py b/src/usethis/_tool/impl/spec/import_linter.py
diff --git a/src/usethis/_tool/rule.py b/src/usethis/_tool/rule.py
diff --git a/tests/docs/test_readme.py b/tests/docs/test_readme.py
diff --git a/tests/usethis/_core/test_core_tool.py b/tests/usethis/_core/test_core_tool.py
diff --git a/tests/usethis/_integrations/pydantic/test_dump.py b/tests/usethis/_integrations/pydantic/test_dump.py
diff --git a/tests/usethis/test_deps.py b/tests/usethis/test_deps.py

Original file line number	Diff line number	Diff line change
`@@ -47,6 +47,6 @@ def get_default_groups_via_uv() -> list[str]:`
`47`	`47`	`PyprojectTOMLManager()[["tool", "uv", "default-groups"]]`
`48`	`48`	`)`
`49`	`49`	`except (KeyError, ValidationError):`
`50`		`- default_groups = []`
	`50`	`+ default_groups: list[str] = []`
`51`	`51`
`52`	`52`	`return default_groups`
Original file line number	Diff line number	Diff line change
`@@ -25,7 +25,7 @@ def use_development_status(`
`25`	`25`	`mgr[["project", "classifiers"]]`
`26`	`26`	`)`
`27`	`27`	`except (KeyError, ValidationError):`
`28`		`- existing_classifiers = []`
	`28`	`+ existing_classifiers: list[str] = []`
`29`	`29`	`existing_status_classifiers = {`
`30`	`30`	`classifier`
`31`	`31`	`for classifier in existing_classifiers`