Feature or enhancement

Let's say you have a dict of some custom annotations like I have in #122262

How users are expected to convert say an annotation dict of {'user': CustomUser[AuthToken], 'auth_callback': Callable[[CustomUser[T]], T]} to string?

There are several ways right now:

1. repr for simple types, which might not work for complex ones

2. cpython/Lib/annotationlib.py

   Lines 466 to 501 in 536bc8a

   	if format == Format.SOURCE:
   	# SOURCE 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(ast.Name(id=name))
   	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)
   	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()
   	}

   but, it requires complex annotate object

3. cpython/Lib/typing.py

   Lines 2955 to 2956 in 536bc8a

   	def _convert_to_source(types):
   	return {n: t if isinstance(t, str) else _type_repr(t) for n, t in types.items()}

   but it is a private API

I propose adding a public and documented API for that.

Linked PRs

• gh-124412: Add helpers for converting annotations to source format #124551