Use TypeAlias where possible for type aliases

[AlexWaygood]

This PR was accomplished using the following steps:

1. Run the below script on typeshed
2. Revert a few places where PEP 612 and PEP 604 combined cause some mypy false-positive errors.
3. Add a few uses of TypeAlias that the script missed, remove a few where the script was overzealous.
4. Manually review the whole thing.

Script I used for step one:

importastimportreimportsubprocessimportsysfromcontextlibimportcontextmanagerfromdataclassesimportdataclassfromitertoolsimportchainfrompathlibimportPathfromtypesimportModuleTypefromtypingimportIterator, NamedTupleFAILURES= []
@dataclassclassNestingCounter:
"""Class to help the PyiVisitor keep track of internal state"""nesting: int=0@contextmanagerdefenabled(self) ->Iterator[None]:
self.nesting+=1try:
yieldfinally:
self.nesting-=1@propertydefactive(self) ->bool:
"""Determine whether the level of nesting is currently non-zero"""returnbool(self.nesting)
deffix_bad_syntax(path: Path) ->None:
withopen(path) asf:
stub=f.read()
lines=stub.splitlines()
tree=ast.parse(stub)
typealias_import_needed=FalseclassStubVisitor(ast.NodeVisitor):
def__init__(self) ->None:
# Mapping of all assignments in the file that could be type aliases# (This excludes assignments to function calls and ellipses, etc.)self.maybe_typealias_assignments: dict[str, ast.Assign] = {}
# Set of all names and attributes that are used as annotations in the fileself.all_annotations: set[str] =set()
self.in_class=NestingCounter()
defvisit_ClassDef(self, node: ast.ClassDef) ->None:
withself.in_class.enabled():
self.generic_visit(node)
defvisit_AnnAssign(self, node: ast.AnnAssign) ->None:
self.all_annotations.add(ast.unparse(node.annotation))
defvisit_Assign(self, node: ast.Assign) ->None:
nonlocaltypealias_import_neededtarget=node.targets[0]
assertisinstance(target, ast.Name)
target_name=target.idif (self.in_class.activeandtarget_name=="__match_args__") or (
target_name=="__all__"andnotself.in_class.active
):
returnassignment=node.valueifisinstance(assignment, (ast.Ellipsis, ast.Call, ast.Num, ast.Str, ast.Bytes)):
returnifisinstance(assignment, ast.Name):
self.maybe_typealias_assignments[target_name] =nodeelifisinstance(assignment, ast.Attribute):
ifisinstance(assignment.value, ast.Name):
self.maybe_typealias_assignments[target_name] =nodeelse:
typealias_import_needed=Truelines[node.lineno-1] =re.sub(f"{target_name} = ", f"{target_name}: TypeAlias = ", lines[node.lineno-1])
defrun(self, tree: ast.AST) ->None:
nonlocaltypealias_import_neededself.visit(tree)
forannotationinself.all_annotations:
ifannotationinself.maybe_typealias_assignments:
node=self.maybe_typealias_assignments[annotation]
typealias_import_needed=Truelines[node.lineno-1] =re.sub(f"{annotation} = ", f"{annotation}: TypeAlias = ", lines[node.lineno-1])
StubVisitor().visit(tree)
ifnottypealias_import_needed:
returntree=ast.parse("\n".join(lines))
typealias_imported=FalseclassTypeAliasImportFinder(ast.NodeVisitor):
defvisit_ImportFrom(self, node: ast.ImportFrom) ->None:
nonlocaltypealias_importedifnode.module!="typing_extensions":
returnifany(cls.name=="TypeAlias"forclsinnode.names):
typealias_imported=TruereturnTypeAliasImportFinder().visit(tree)
ifnottypealias_imported:
lines= ["from typing_extensions import TypeAlias"] +lineswithopen(path, "w") asf:
f.write("\n".join(lines) +"\n")
defmain() ->None:
print("STARTING RUN: Will attempt to fix new syntax in the stubs directory...\n\n")
forpathinchain(Path("stdlib").rglob("*.pyi"), Path("stubs").rglob("*.pyi")):
if"@python2"inpath.parts:
continueprint(f"Attempting to convert {path} to new syntax.")
fix_bad_syntax(path)
print("\n\nSTARTING ISORT...\n\n")
subprocess.run([sys.executable, "-m", "isort", "."])
print("\n\nSTARTING BLACK...\n\n")
subprocess.run([sys.executable, "-m", "black", "."])
ifFAILURES:
print("\n\nFAILED to convert the following files to new syntax:\n")
forpathinFAILURES:
print(f"- {path}")
else:
print("\n\nThere were ZERO failures in converting to new syntax. HOORAY!!\n\n")
print('\n\nRunning "check_new_syntax.py"...\n\n')
subprocess.run([sys.executable, "tests/check_new_syntax.py"])
if__name__=="__main__":
main()

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[JelleZijlstra]

Looks good, thanks for doing all this!

[JelleZijlstra]

This looks a bit odd but seems like they're indeed intended as aliases.

[JelleZijlstra]

good catch, though maybe we should do from builtins import list as _list instead

[AlexWaygood]

Done in #7634!