annotationlib.py

"""Helpers for introspecting and wrapping annotations."""

import ast
import builtins
import enum
import functools
import keyword
import sys
import types

__all__ = [
    "Format",
    "ForwardRef",
    "call_annotate_function",
    "call_evaluate_function",
    "get_annotate_function",
    "get_annotations",
    "annotations_to_string",
    "value_to_string",
]


class Format(enum.IntEnum):
    VALUE = 1
    VALUE_WITH_FAKE_GLOBALS = 2
    FORWARDREF = 3
    STRING = 4


_Union = None
_sentinel = object()

# Slots shared by ForwardRef and _Stringifier. The __forward__ names must be
# preserved for compatibility with the old typing.ForwardRef class. The remaining
# names are private.
_SLOTS = (
    "__forward_evaluated__",
    "__forward_value__",
    "__forward_is_argument__",
    "__forward_is_class__",
    "__forward_module__",
    "__weakref__",
    "__arg__",
    "__ast_node__",
    "__code__",
    "__globals__",
    "__owner__",
    "__cell__",
    "__stringifier_dict__",
)


class ForwardRef:
    """Wrapper that holds a forward reference.

    Constructor arguments:
    * arg: a string representing the code to be evaluated.
    * module: the module where the forward reference was created.
      Must be a string, not a module object.
    * owner: The owning object (module, class, or function).
    * is_argument: Does nothing, retained for compatibility.
    * is_class: True if the forward reference was created in class scope.

    """

    __slots__ = _SLOTS

    def __init__(
        self,
        arg,
        *,
        module=None,
        owner=None,
        is_argument=True,
        is_class=False,
    ):
        if not isinstance(arg, str):
            raise TypeError(f"Forward reference must be a string -- got {arg!r}")

        self.__arg__ = arg
        self.__forward_evaluated__ = False
        self.__forward_value__ = None
        self.__forward_is_argument__ = is_argument
        self.__forward_is_class__ = is_class
        self.__forward_module__ = module
        self.__code__ = None
        self.__ast_node__ = None
        self.__globals__ = None
        self.__cell__ = None
        self.__owner__ = owner

    def __init_subclass__(cls, /, *args, **kwds):
        raise TypeError("Cannot subclass ForwardRef")

    def evaluate(self, *, globals=None, locals=None, type_params=None, owner=None):
        """Evaluate the forward reference and return the value.

        If the forward reference cannot be evaluated, raise an exception.
        """
        if self.__forward_evaluated__:
            return self.__forward_value__
        if self.__cell__ is not None:
            try:
                value = self.__cell__.cell_contents
            except ValueError:
                pass
            else:
                self.__forward_evaluated__ = True
                self.__forward_value__ = value
                return value
        if owner is None:
            owner = self.__owner__

        if globals is None and self.__forward_module__ is not None:
            globals = getattr(
                sys.modules.get(self.__forward_module__, None), "__dict__", None
            )
        if globals is None:
            globals = self.__globals__
        if globals is None:
            if isinstance(owner, type):
                module_name = getattr(owner, "__module__", None)
                if module_name:
                    module = sys.modules.get(module_name, None)
                    if module:
                        globals = getattr(module, "__dict__", None)
            elif isinstance(owner, types.ModuleType):
                globals = getattr(owner, "__dict__", None)
            elif callable(owner):
                globals = getattr(owner, "__globals__", None)

        # If we pass None to eval() below, the globals of this module are used.
        if globals is None:
            globals = {}

        if locals is None:
            locals = {}
            if isinstance(owner, type):
                locals.update(vars(owner))

        if type_params is None and owner is not None:
            # "Inject" type parameters into the local namespace
            # (unless they are shadowed by assignments *in* the local namespace),
            # as a way of emulating annotation scopes when calling `eval()`
            type_params = getattr(owner, "__type_params__", None)

        # type parameters require some special handling,
        # as they exist in their own scope
        # but `eval()` does not have a dedicated parameter for that scope.
        # For classes, names in type parameter scopes should override
        # names in the global scope (which here are called `localns`!),
        # but should in turn be overridden by names in the class scope
        # (which here are called `globalns`!)
        if type_params is not None:
            globals = dict(globals)
            locals = dict(locals)
            for param in type_params:
                param_name = param.__name__
                if not self.__forward_is_class__ or param_name not in globals:
                    globals[param_name] = param
                    locals.pop(param_name, None)

        arg = self.__forward_arg__
        if arg.isidentifier() and not keyword.iskeyword(arg):
            if arg in locals:
                value = locals[arg]
            elif arg in globals:
                value = globals[arg]
            elif hasattr(builtins, arg):
                return getattr(builtins, arg)
            else:
                raise NameError(arg)
        else:
            code = self.__forward_code__
            value = eval(code, globals=globals, locals=locals)
        self.__forward_evaluated__ = True
        self.__forward_value__ = value
        return value

    def _evaluate(self, globalns, localns, type_params=_sentinel, *, recursive_guard):
        import typing
        import warnings

        if type_params is _sentinel:
            typing._deprecation_warning_for_no_type_params_passed(
                "typing.ForwardRef._evaluate"
            )
            type_params = ()
        warnings._deprecated(
            "ForwardRef._evaluate",
            "{name} is a private API and is retained for compatibility, but will be removed"
            " in Python 3.16. Use ForwardRef.evaluate() or typing.evaluate_forward_ref() instead.",
            remove=(3, 16),
        )
        return typing.evaluate_forward_ref(
            self,
            globals=globalns,
            locals=localns,
            type_params=type_params,
            _recursive_guard=recursive_guard,
        )

    @property
    def __forward_arg__(self):
        if self.__arg__ is not None:
            return self.__arg__
        if self.__ast_node__ is not None:
            self.__arg__ = ast.unparse(self.__ast_node__)
            return self.__arg__
        raise AssertionError(
            "Attempted to access '__forward_arg__' on an uninitialized ForwardRef"
        )

    @property
    def __forward_code__(self):
        if self.__code__ is not None:
            return self.__code__
        arg = self.__forward_arg__
        # If we do `def f(*args: *Ts)`, then we'll have `arg = '*Ts'`.
        # Unfortunately, this isn't a valid expression on its own, so we
        # do the unpacking manually.
        if arg.startswith("*"):
            arg_to_compile = f"({arg},)[0]"  # E.g. (*Ts,)[0] or (*tuple[int, int],)[0]
        else:
            arg_to_compile = arg
        try:
            self.__code__ = compile(arg_to_compile, "<string>", "eval")
        except SyntaxError:
            raise SyntaxError(f"Forward reference must be an expression -- got {arg!r}")
        return self.__code__

    def __eq__(self, other):
        if not isinstance(other, ForwardRef):
            return NotImplemented
        if self.__forward_evaluated__ and other.__forward_evaluated__:
            return (
                self.__forward_arg__ == other.__forward_arg__
                and self.__forward_value__ == other.__forward_value__
            )
        return (
            self.__forward_arg__ == other.__forward_arg__
            and self.__forward_module__ == other.__forward_module__
        )

    def __hash__(self):
        return hash((self.__forward_arg__, self.__forward_module__))

    def __or__(self, other):
        global _Union
        if _Union is None:
            from typing import Union as _Union
        return _Union[self, other]

    def __ror__(self, other):
        global _Union
        if _Union is None:
            from typing import Union as _Union
        return _Union[other, self]

    def __repr__(self):
        if self.__forward_module__ is None:
            module_repr = ""
        else:
            module_repr = f", module={self.__forward_module__!r}"
        return f"ForwardRef({self.__forward_arg__!r}{module_repr})"


class _Stringifier:
    # Must match the slots on ForwardRef, so we can turn an instance of one into an
    # instance of the other in place.
    __slots__ = _SLOTS

    def __init__(
        self,
        node,
        globals=None,
        owner=None,
        is_class=False,
        cell=None,
        *,
        stringifier_dict,
    ):
        # Either an AST node or a simple str (for the common case where a ForwardRef
        # represent a single name).
        assert isinstance(node, (ast.AST, str))
        self.__arg__ = None
        self.__forward_evaluated__ = False
        self.__forward_value__ = None
        self.__forward_is_argument__ = False
        self.__forward_is_class__ = is_class
        self.__forward_module__ = None
        self.__code__ = None
        self.__ast_node__ = node
        self.__globals__ = globals
        self.__cell__ = cell
        self.__owner__ = owner
        self.__stringifier_dict__ = stringifier_dict

    def __convert_to_ast(self, other):
        if isinstance(other, _Stringifier):
            if isinstance(other.__ast_node__, str):
                return ast.Name(id=other.__ast_node__)
            return other.__ast_node__
        elif isinstance(other, slice):
            return ast.Slice(
                lower=(
                    self.__convert_to_ast(other.start)
                    if other.start is not None
                    else None
                ),
                upper=(
                    self.__convert_to_ast(other.stop)
                    if other.stop is not None
                    else None
                ),
                step=(
                    self.__convert_to_ast(other.step)
                    if other.step is not None
                    else None
                ),
            )
        else:
            return ast.Constant(value=other)

    def __get_ast(self):
        node = self.__ast_node__
        if isinstance(node, str):
            return ast.Name(id=node)
        return node

    def __make_new(self, node):
        stringifier = _Stringifier(
            node,
            self.__globals__,
            self.__owner__,
            self.__forward_is_class__,
            stringifier_dict=self.__stringifier_dict__,
        )
        self.__stringifier_dict__.stringifiers.append(stringifier)
        return stringifier

    # Must implement this since we set __eq__. We hash by identity so that
    # stringifiers in dict keys are kept separate.
    def __hash__(self):
        return id(self)

    def __getitem__(self, other):
        # Special case, to avoid stringifying references to class-scoped variables
        # as '__classdict__["x"]'.
        if self.__ast_node__ == "__classdict__":
            raise KeyError
        if isinstance(other, tuple):
            elts = [self.__convert_to_ast(elt) for elt in other]
            other = ast.Tuple(elts)
        else:
            other = self.__convert_to_ast(other)
        assert isinstance(other, ast.AST), repr(other)
        return self.__make_new(ast.Subscript(self.__get_ast(), other))

    def __getattr__(self, attr):
        return self.__make_new(ast.Attribute(self.__get_ast(), attr))

    def __call__(self, *args, **kwargs):
        return self.__make_new(
            ast.Call(
                self.__get_ast(),
                [self.__convert_to_ast(arg) for arg in args],
                [
                    ast.keyword(key, self.__convert_to_ast(value))
                    for key, value in kwargs.items()
                ],
            )
        )

    def __iter__(self):
        yield self.__make_new(ast.Starred(self.__get_ast()))

    def __repr__(self):
        if isinstance(self.__ast_node__, str):
            return self.__ast_node__
        return ast.unparse(self.__ast_node__)

    def __format__(self, format_spec):
        raise TypeError("Cannot stringify annotation containing string formatting")

    def _make_binop(op: ast.AST):
        def binop(self, other):
            return self.__make_new(
                ast.BinOp(self.__get_ast(), op, self.__convert_to_ast(other))
            )

        return binop

    __add__ = _make_binop(ast.Add())
    __sub__ = _make_binop(ast.Sub())
    __mul__ = _make_binop(ast.Mult())
    __matmul__ = _make_binop(ast.MatMult())
    __truediv__ = _make_binop(ast.Div())
    __mod__ = _make_binop(ast.Mod())
    __lshift__ = _make_binop(ast.LShift())
    __rshift__ = _make_binop(ast.RShift())
    __or__ = _make_binop(ast.BitOr())
    __xor__ = _make_binop(ast.BitXor())
    __and__ = _make_binop(ast.BitAnd())
    __floordiv__ = _make_binop(ast.FloorDiv())
    __pow__ = _make_binop(ast.Pow())

    del _make_binop

    def _make_rbinop(op: ast.AST):
        def rbinop(self, other):
            return self.__make_new(
                ast.BinOp(self.__convert_to_ast(other), op, self.__get_ast())
            )

        return rbinop

    __radd__ = _make_rbinop(ast.Add())
    __rsub__ = _make_rbinop(ast.Sub())
    __rmul__ = _make_rbinop(ast.Mult())
    __rmatmul__ = _make_rbinop(ast.MatMult())
    __rtruediv__ = _make_rbinop(ast.Div())
    __rmod__ = _make_rbinop(ast.Mod())
    __rlshift__ = _make_rbinop(ast.LShift())
    __rrshift__ = _make_rbinop(ast.RShift())
    __ror__ = _make_rbinop(ast.BitOr())
    __rxor__ = _make_rbinop(ast.BitXor())
    __rand__ = _make_rbinop(ast.BitAnd())
    __rfloordiv__ = _make_rbinop(ast.FloorDiv())
    __rpow__ = _make_rbinop(ast.Pow())

    del _make_rbinop

    def _make_compare(op):
        def compare(self, other):
            return self.__make_new(
                ast.Compare(
                    left=self.__get_ast(),
                    ops=[op],
                    comparators=[self.__convert_to_ast(other)],
                )
            )

        return compare

    __lt__ = _make_compare(ast.Lt())
    __le__ = _make_compare(ast.LtE())
    __eq__ = _make_compare(ast.Eq())
    __ne__ = _make_compare(ast.NotEq())
    __gt__ = _make_compare(ast.Gt())
    __ge__ = _make_compare(ast.GtE())

    del _make_compare

    def _make_unary_op(op):
        def unary_op(self):
            return self.__make_new(ast.UnaryOp(op, self.__get_ast()))

        return unary_op

    __invert__ = _make_unary_op(ast.Invert())
    __pos__ = _make_unary_op(ast.UAdd())
    __neg__ = _make_unary_op(ast.USub())

    del _make_unary_op


class _StringifierDict(dict):
    def __init__(self, namespace, globals=None, owner=None, is_class=False):
        super().__init__(namespace)
        self.namespace = namespace
        self.globals = globals
        self.owner = owner
        self.is_class = is_class
        self.stringifiers = []

    def __missing__(self, key):
        fwdref = _Stringifier(
            key,
            globals=self.globals,
            owner=self.owner,
            is_class=self.is_class,
            stringifier_dict=self,
        )
        self.stringifiers.append(fwdref)
        return fwdref


def call_evaluate_function(evaluate, format, *, owner=None):
    """Call an evaluate function. Evaluate functions are normally generated for
    the value of type aliases and the bounds, constraints, and defaults of
    type parameter objects.
    """
    return call_annotate_function(evaluate, format, owner=owner, _is_evaluate=True)


def call_annotate_function(annotate, format, *, owner=None, _is_evaluate=False):
    """Call an __annotate__ function. __annotate__ functions are normally
    generated by the compiler to defer the evaluation of annotations. They
    can be called with any of the format arguments in the Format enum, but
    compiler-generated __annotate__ functions only support the VALUE format.
    This function provides additional functionality to call __annotate__
    functions with the FORWARDREF and STRING formats.

    *annotate* must be an __annotate__ function, which takes a single argument
    and returns a dict of annotations.

    *format* must be a member of the Format enum or one of the corresponding
    integer values.

    *owner* can be the object that owns the annotations (i.e., the module,
    class, or function that the __annotate__ function derives from). With the
    FORWARDREF format, it is used to provide better evaluation capabilities
    on the generated ForwardRef objects.

    """
    if format == Format.VALUE_WITH_FAKE_GLOBALS:
        raise ValueError("The VALUE_WITH_FAKE_GLOBALS format is for internal use only")
    try:
        return annotate(format)
    except NotImplementedError:
        pass
    if format == Format.STRING:
        # STRING is implemented by calling the annotate function in a special
        # environment where every name lookup results in an instance of _Stringifier.
        # _Stringifier supports every dunder operation and returns a new _Stringifier.
        # At the end, we get a dictionary that mostly contains _Stringifier objects (or
        # possibly constants if the annotate function uses them directly). We then
        # convert each of those into a string to get an approximation of the
        # original source.
        globals = _StringifierDict({})
        if annotate.__closure__:
            freevars = annotate.__code__.co_freevars
            new_closure = []
            for i, cell in enumerate(annotate.__closure__):
                if i < len(freevars):
                    name = freevars[i]
                else:
                    name = "__cell__"
                fwdref = _Stringifier(name, stringifier_dict=globals)
                new_closure.append(types.CellType(fwdref))
            closure = tuple(new_closure)
        else:
            closure = None
        func = types.FunctionType(
            annotate.__code__,
            globals,
            closure=closure,
            argdefs=annotate.__defaults__,
            kwdefaults=annotate.__kwdefaults__,
        )
        annos = func(Format.VALUE_WITH_FAKE_GLOBALS)
        if _is_evaluate:
            return annos if isinstance(annos, str) else repr(annos)
        return {
            key: val if isinstance(val, str) else repr(val)
            for key, val in annos.items()
        }
    elif format == Format.FORWARDREF:
        # FORWARDREF is implemented similarly to STRING, but there are two changes,
        # at the beginning and the end of the process.
        # First, while STRING uses an empty dictionary as the namespace, so that all
        # name lookups result in _Stringifier objects, FORWARDREF uses the globals
        # and builtins, so that defined names map to their real values.
        # Second, instead of returning strings, we want to return either real values
        # or ForwardRef objects. To do this, we keep track of all _Stringifier objects
        # created while the annotation is being evaluated, and at the end we convert
        # them all to ForwardRef objects by assigning to __class__. To make this
        # technique work, we have to ensure that the _Stringifier and ForwardRef
        # classes share the same attributes.
        # We use this technique because while the annotations are being evaluated,
        # we want to support all operations that the language allows, including even
        # __getattr__ and __eq__, and return new _Stringifier objects so we can accurately
        # reconstruct the source. But in the dictionary that we eventually return, we
        # want to return objects with more user-friendly behavior, such as an __eq__
        # that returns a bool and an defined set of attributes.
        namespace = {**annotate.__builtins__, **annotate.__globals__}
        is_class = isinstance(owner, type)
        globals = _StringifierDict(namespace, annotate.__globals__, owner, is_class)
        if annotate.__closure__:
            freevars = annotate.__code__.co_freevars
            new_closure = []
            for i, cell in enumerate(annotate.__closure__):
                try:
                    cell.cell_contents
                except ValueError:
                    if i < len(freevars):
                        name = freevars[i]
                    else:
                        name = "__cell__"
                    fwdref = _Stringifier(
                        name,
                        cell=cell,
                        owner=owner,
                        globals=annotate.__globals__,
                        is_class=is_class,
                        stringifier_dict=globals,
                    )
                    globals.stringifiers.append(fwdref)
                    new_closure.append(types.CellType(fwdref))
                else:
                    new_closure.append(cell)
            closure = tuple(new_closure)
        else:
            closure = None
        func = types.FunctionType(
            annotate.__code__,
            globals,
            closure=closure,
            argdefs=annotate.__defaults__,
            kwdefaults=annotate.__kwdefaults__,
        )
        result = func(Format.VALUE_WITH_FAKE_GLOBALS)
        for obj in globals.stringifiers:
            obj.__class__ = ForwardRef
            obj.__stringifier_dict__ = None  # not needed for ForwardRef
            if isinstance(obj.__ast_node__, str):
                obj.__arg__ = obj.__ast_node__
                obj.__ast_node__ = None
        return result
    elif format == Format.VALUE:
        # Should be impossible because __annotate__ functions must not raise
        # NotImplementedError for this format.
        raise RuntimeError("annotate function does not support VALUE format")
    else:
        raise ValueError(f"Invalid format: {format!r}")


# We use the descriptors from builtins.type instead of accessing
# .__annotations__ and .__annotate__ directly on class objects, because
# otherwise we could get wrong results in some cases involving metaclasses.
# See PEP 749.
_BASE_GET_ANNOTATE = type.__dict__["__annotate__"].__get__
_BASE_GET_ANNOTATIONS = type.__dict__["__annotations__"].__get__


def get_annotate_function(obj):
    """Get the __annotate__ function for an object.

    obj may be a function, class, or module, or a user-defined type with
    an `__annotate__` attribute.

    Returns the __annotate__ function or None.
    """
    if isinstance(obj, type):
        try:
            return _BASE_GET_ANNOTATE(obj)
        except AttributeError:
            # AttributeError is raised for static types.
            return None
    return getattr(obj, "__annotate__", None)


def get_annotations(
    obj, *, globals=None, locals=None, eval_str=False, format=Format.VALUE
):
    """Compute the annotations dict for an object.

    obj may be a callable, class, or module.
    Passing in an object of any other type raises TypeError.

    Returns a dict.  get_annotations() returns a new dict every time
    it's called; calling it twice on the same object will return two
    different but equivalent dicts.

    This function handles several details for you:

      * If eval_str is true, values of type str will
        be un-stringized using eval().  This is intended
        for use with stringized annotations
        ("from __future__ import annotations").
      * If obj doesn't have an annotations dict, returns an
        empty dict.  (Functions and methods always have an
        annotations dict; classes, modules, and other types of
        callables may not.)
      * Ignores inherited annotations on classes.  If a class
        doesn't have its own annotations dict, returns an empty dict.
      * All accesses to object members and dict values are done
        using getattr() and dict.get() for safety.
      * Always, always, always returns a freshly-created dict.

    eval_str controls whether or not values of type str are replaced
    with the result of calling eval() on those values:

      * If eval_str is true, eval() is called on values of type str.
      * If eval_str is false (the default), values of type str are unchanged.

    globals and locals are passed in to eval(); see the documentation
    for eval() for more information.  If either globals or locals is
    None, this function may replace that value with a context-specific
    default, contingent on type(obj):

      * If obj is a module, globals defaults to obj.__dict__.
      * If obj is a class, globals defaults to
        sys.modules[obj.__module__].__dict__ and locals
        defaults to the obj class namespace.
      * If obj is a callable, globals defaults to obj.__globals__,
        although if obj is a wrapped function (using
        functools.update_wrapper()) it is first unwrapped.
    """
    if eval_str and format != Format.VALUE:
        raise ValueError("eval_str=True is only supported with format=Format.VALUE")

    match format:
        case Format.VALUE:
            # For VALUE, we only look at __annotations__
            ann = _get_dunder_annotations(obj)
        case Format.FORWARDREF:
            # For FORWARDREF, we use __annotations__ if it exists
            try:
                return dict(_get_dunder_annotations(obj))
            except NameError:
                pass

            # But if __annotations__ threw a NameError, we try calling __annotate__
            ann = _get_and_call_annotate(obj, format)
            if ann is not None:
                return ann

            # If that didn't work either, we have a very weird object: evaluating
            # __annotations__ threw NameError and there is no __annotate__. In that case,
            # we fall back to trying __annotations__ again.
            return dict(_get_dunder_annotations(obj))
        case Format.STRING:
            # For STRING, we try to call __annotate__
            ann = _get_and_call_annotate(obj, format)
            if ann is not None:
                return ann
            # But if we didn't get it, we use __annotations__ instead.
            ann = _get_dunder_annotations(obj)
            return annotations_to_string(ann)
        case Format.VALUE_WITH_FAKE_GLOBALS:
            raise ValueError("The VALUE_WITH_FAKE_GLOBALS format is for internal use only")
        case _:
            raise ValueError(f"Unsupported format {format!r}")

    if not ann:
        return {}

    if not eval_str:
        return dict(ann)

    if isinstance(obj, type):
        # class
        obj_globals = None
        module_name = getattr(obj, "__module__", None)
        if module_name:
            module = sys.modules.get(module_name, None)
            if module:
                obj_globals = getattr(module, "__dict__", None)
        obj_locals = dict(vars(obj))
        unwrap = obj
    elif isinstance(obj, types.ModuleType):
        # module
        obj_globals = getattr(obj, "__dict__")
        obj_locals = None
        unwrap = None
    elif callable(obj):
        # this includes types.Function, types.BuiltinFunctionType,
        # types.BuiltinMethodType, functools.partial, functools.singledispatch,
        # "class funclike" from Lib/test/test_inspect... on and on it goes.
        obj_globals = getattr(obj, "__globals__", None)
        obj_locals = None
        unwrap = obj
    elif ann is not None:
        obj_globals = obj_locals = unwrap = None
    else:
        raise TypeError(f"{obj!r} is not a module, class, or callable.")

    if unwrap is not None:
        while True:
            if hasattr(unwrap, "__wrapped__"):
                unwrap = unwrap.__wrapped__
                continue
            if isinstance(unwrap, functools.partial):
                unwrap = unwrap.func
                continue
            break
        if hasattr(unwrap, "__globals__"):
            obj_globals = unwrap.__globals__

    if globals is None:
        globals = obj_globals
    if locals is None:
        locals = obj_locals

    # "Inject" type parameters into the local namespace
    # (unless they are shadowed by assignments *in* the local namespace),
    # as a way of emulating annotation scopes when calling `eval()`
    if type_params := getattr(obj, "__type_params__", ()):
        if locals is None:
            locals = {}
        locals = {param.__name__: param for param in type_params} | locals

    return_value = {
        key: value if not isinstance(value, str) else eval(value, globals, locals)
        for key, value in ann.items()
    }
    return return_value


def value_to_string(value):
    """Convert a Python value to a format suitable for use with the STRING format.

    This is inteded as a helper for tools that support the STRING format but do
    not have access to the code that originally produced the annotations. It uses
    repr() for most objects.

    """
    if isinstance(value, type):
        if value.__module__ == "builtins":
            return value.__qualname__
        return f"{value.__module__}.{value.__qualname__}"
    if value is ...:
        return "..."
    if isinstance(value, (types.FunctionType, types.BuiltinFunctionType)):
        return value.__name__
    return repr(value)


def annotations_to_string(annotations):
    """Convert an annotation dict containing values to approximately the STRING format."""
    return {
        n: t if isinstance(t, str) else value_to_string(t)
        for n, t in annotations.items()
    }


def _get_and_call_annotate(obj, format):
    annotate = get_annotate_function(obj)
    if annotate is not None:
        ann = call_annotate_function(annotate, format, owner=obj)
        if not isinstance(ann, dict):
            raise ValueError(f"{obj!r}.__annotate__ returned a non-dict")
        return dict(ann)
    return None


def _get_dunder_annotations(obj):
    if isinstance(obj, type):
        try:
            ann = _BASE_GET_ANNOTATIONS(obj)
        except AttributeError:
            # For static types, the descriptor raises AttributeError.
            return {}
    else:
        ann = getattr(obj, "__annotations__", None)
        if ann is None:
            return {}

    if not isinstance(ann, dict):
        raise ValueError(f"{obj!r}.__annotations__ is neither a dict nor None")
    return dict(ann)