Fix for typing.get_type_hints() on Python 3.9 or lower (#4228)

* fix

* fix docstring

* type hint fix

* fix test

* Update gradio/utils.py

Co-authored-by: Aarni Koskela <akx@iki.fi>

* fix indentation

---------

Co-authored-by: Aarni Koskela <akx@iki.fi>

CHANGELOG.md

@@ -6,12 +6,14 @@
 - Added `format` argument to `Audio` component by [@freddyaboulton](https://github.com/freddyaboulton) in [PR 4178](https://github.com/gradio-app/gradio/pull/4178)
 - Add JS client code snippets to use via api page by [@aliabd](https://github.com/aliabd) in [PR 3927](https://github.com/gradio-app/gradio/pull/3927).
 
+
 ## Bug Fixes:
 
 - Fix "TypeError: issubclass() arg 1 must be a class" When use Optional[Types] by [@lingfengchencn](https://github.com/lingfengchencn) in [PR 4200](https://github.com/gradio-app/gradio/pull/4200). 
 - Gradio will no longer send any analytics if analytics are disabled with the GRADIO_ANALYTICS_ENABLED environment variable. By [@akx](https://github.com/akx) in [PR 4194](https://github.com/gradio-app/gradio/pull/4194)
 - The deprecation warnings for kwargs now show the actual stack level for the invocation, by [@akx](https://github.com/akx) in [PR 4203](https://github.com/gradio-app/gradio/pull/4203).
 - Fix "TypeError: issubclass() arg 1 must be a class" When use Optional[Types] by [@lingfengchencn](https://github.com/lingfengchencn) in [PR 4200](https://github.com/gradio-app/gradio/pull/4200). 
+- Fixes a bug with typing.get_type_hints() on Python 3.9 by [@abidlabs](https://github.com/abidlabs) in [PR 4228](https://github.com/gradio-app/gradio/pull/4228).
 
 ## Other Changes:
 

gradio/utils.py

@@ -683,11 +683,41 @@ def get_cancel_function(
 
 
 def get_type_hints(fn):
+    # Importing gradio with the canonical abbreviation. Used in typing._eval_type.
+    import gradio as gr  # noqa: F401
+    from gradio import Request  # noqa: F401
+
     if inspect.isfunction(fn) or inspect.ismethod(fn):
-        return typing.get_type_hints(fn)
+        pass
     elif callable(fn):
-        return typing.get_type_hints(fn.__call__)
-    return {}
+        fn = fn.__call__
+    else:
+        return {}
+
+    try:
+        return typing.get_type_hints(fn)
+    except TypeError:
+        # On Python 3.9 or earlier, get_type_hints throws a TypeError if the function
+        # has a type annotation that include "|". We resort to parsing the signature
+        # manually using inspect.signature.
+        type_hints = {}
+        sig = inspect.signature(fn)
+        for name, param in sig.parameters.items():
+            if param.annotation is inspect.Parameter.empty:
+                continue
+            if "|" in str(param.annotation):
+                continue
+            # To convert the string annotation to a class, we use the
+            # internal typing._eval_type function. This is not ideal, but
+            # it's the only way to do it without eval-ing the string.
+            # Since the API is internal, it may change in the future.
+            try:
+                type_hints[name] = typing._eval_type(  # type: ignore
+                    typing.ForwardRef(param.annotation), globals(), locals()
+                )
+            except (NameError, TypeError):
+                pass
+        return type_hints
 
 
 def is_special_typed_parameter(name, parameter_types):

test/test_utils.py

@@ -1,9 +1,10 @@
+from __future__ import annotations
+
 import copy
 import os
 import sys
 import unittest.mock as mock
 import warnings
-from typing import List
 from unittest.mock import MagicMock
 
 import pytest
@@ -570,7 +571,7 @@ class TestGetTypeHints:
         assert len(get_type_hints(GenericObject())) == 0
 
     def test_is_special_typed_parameter(self):
-        def func(a: List[str], b: Literal["a", "b"], c, d: Request):
+        def func(a: list[str], b: Literal["a", "b"], c, d: Request):
             pass
 
         hints = get_type_hints(func)
@@ -579,6 +580,15 @@ class TestGetTypeHints:
         assert not is_special_typed_parameter("c", hints)
         assert is_special_typed_parameter("d", hints)
 
+    def test_is_special_typed_parameter_with_pipe(self):
+        def func(a: Request, b: str | int, c: list[str]):
+            pass
+
+        hints = get_type_hints(func)
+        assert is_special_typed_parameter("a", hints)
+        assert not is_special_typed_parameter("b", hints)
+        assert not is_special_typed_parameter("c", hints)
+
 
 class TestCheckFunctionInputsMatch:
     def test_check_function_inputs_match(self):