Make st.help more resilient with conditional members (#8228)

## Describe your changes

`st.help` leverages `dir(object)` to determine the members in the object
to expose to the docstring. If an object makes a member conditional
based on internal state, `st.help` can throw an `AttributeError`.
Ideally, in these cases, the developer of the object would implement the
`__dir__` method to handle conditional members, but Streamlit can be
more resilient in handling this situation.

The example that brought this up was in sklearn, and I created
scikit-learn/scikit-learn#28558 with them to
better handle this scenario.

## Testing Plan

- Unit Tests should cover the change with the member available and
unavailable

---

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project are made under the Apache 2.0 license.

lib/streamlit/elements/doc_string.py

@@ -514,30 +514,35 @@ def _get_members(obj):
         if attr_name.startswith("_"):
             continue
 
-        is_computed_value = _is_computed_property(obj, attr_name)
+        try:
+            is_computed_value = _is_computed_property(obj, attr_name)
+            if is_computed_value:
+                parent_attr = getattr(obj.__class__, attr_name)
 
-        if is_computed_value:
-            parent_attr = getattr(obj.__class__, attr_name)
+                member_type = "property"
 
-            member_type = "property"
-
-            weight = 0
-            member_docs = _get_docstring(parent_attr)
-            member_value = None
-        else:
-            attr_value = getattr(obj, attr_name)
-            weight = _get_weight(attr_value)
-
-            human_readable_value = _get_human_readable_value(attr_value)
-
-            member_type = _get_type_as_str(attr_value)
-
-            if human_readable_value is None:
-                member_docs = _get_docstring(attr_value)
+                weight = 0
+                member_docs = _get_docstring(parent_attr)
                 member_value = None
             else:
-                member_docs = None
-                member_value = human_readable_value
+                attr_value = getattr(obj, attr_name)
+                weight = _get_weight(attr_value)
+
+                human_readable_value = _get_human_readable_value(attr_value)
+
+                member_type = _get_type_as_str(attr_value)
+
+                if human_readable_value is None:
+                    member_docs = _get_docstring(attr_value)
+                    member_value = None
+                else:
+                    member_docs = None
+                    member_value = human_readable_value
+        except AttributeError:
+            # If there's an AttributeError, we can just skip it.
+            # This can happen when members are exposed with `dir()`
+            # but are conditionally unavailable.
+            continue
 
         if member_type == "module":
             # Don't pollute the output with all imported modules.

lib/tests/streamlit/elements/doc_string_test.py

@@ -33,6 +33,21 @@ def patch_varname_getter():
     )
 
 
+class ConditionalHello:
+    def __init__(self, available, ExceptionType=AttributeError):
+        self.available = available
+        self.ExceptionType = ExceptionType
+
+    def __getattribute__(self, name):
+        if name == "say_hello" and not self.available:
+            raise self.ExceptionType(f"{name} is not accessible when x is even")
+        else:
+            return object.__getattribute__(self, name)
+
+    def say_hello(self):
+        pass
+
+
 class StHelpAPITest(DeltaGeneratorTestCase):
     """Test Public Streamlit Public APIs."""
 
@@ -48,3 +63,29 @@ def test_st_help(self):
             el.doc_string.startswith("Change the current working directory")
         )
         self.assertEqual(f"posix.chdir(path)", el.value)
+
+    def test_st_help_with_available_conditional_members(self):
+        """Test st.help with conditional members available"""
+
+        st.help(ConditionalHello(True))
+        el = self.get_delta_from_queue().new_element.doc_string
+        self.assertEqual("ConditionalHello", el.type)
+        member_names = [member.name for member in el.members]
+        self.assertIn("say_hello", member_names)
+
+    def test_st_help_with_unavailable_conditional_members(self):
+        """Test st.help with conditional members not available
+        via AttributeError"""
+
+        st.help(ConditionalHello(False))
+        el = self.get_delta_from_queue().new_element.doc_string
+        self.assertEqual("ConditionalHello", el.type)
+        member_names = [member.name for member in el.members]
+        self.assertNotIn("say_hello", member_names)
+
+    def test_st_help_with_erroneous_members(self):
+        """Test st.help with conditional members not available
+        via some non-AttributeError exception"""
+
+        with self.assertRaises(ValueError):
+            st.help(ConditionalHello(False, ValueError))