Python: Treat a single string passed to Message as one text content

python/packages/core/agent_framework/_types.py

@@ -56,11 +56,16 @@ def _parse_content_list(contents_data: Sequence[Any]) -> list[Content]:
     """Parse a list of content data into appropriate Content objects.
 
     Args:
-        contents_data: List of content data (strings, dicts, or already constructed objects)
+        contents_data: List of content data (strings, dicts, or already constructed objects).
+            A single string is treated as one text item.
 
     Returns:
         List of Content objects with unknown types logged and ignored
     """
+    if isinstance(contents_data, str):
+        # A string is itself a sequence of strings, so iterating it would create one text
+        # content per character.
+        contents_data = [contents_data]
     contents: list[Content] = []
     for content_data in contents_data:
         if content_data is None:
@@ -2072,7 +2077,8 @@ def __init__(
         Args:
             role: The role of the author of the message (e.g., "user", "assistant", "system", "tool").
             contents: A sequence of content items. Can be Content objects, strings (auto-converted
-                to TextContent), or dicts (parsed via Content.from_dict). Defaults to empty list.
+                to TextContent), or dicts (parsed via Content.from_dict). A single string is
+                treated as one text item. Defaults to empty list.
 
         Keyword Args:
             author_name: Optional name of the author of the message.

python/packages/core/tests/core/test_types.py

@@ -1167,6 +1167,25 @@ def test_chat_message_text():
     assert isinstance(message.contents[0], Content)
 
 
+@pytest.mark.parametrize(
+    "message",
+    [Message("user", "Hello, how are you?"), Message(role="user", contents="Hello, how are you?")],
+    ids=["positional", "keyword"],
+)
+def test_chat_message_with_single_string_contents(message: Message) -> None:
+    """A bare string is one text content, not a sequence of single-character contents."""
+    assert len(message.contents) == 1
+    assert message.contents[0].type == "text"
+    assert message.text == "Hello, how are you?"
+
+
+def test_chat_message_with_empty_string_contents() -> None:
+    message = Message("user", "")
+
+    assert len(message.contents) == 1
+    assert message.text == ""
+
+
 def test_chat_message_contents():
     """Test the Message class to ensure it initializes correctly with contents."""
     # Create a Message with a role and multiple contents
@@ -4553,6 +4572,15 @@ def test_parse_content_list_with_dicts():
     assert result[0].text == "hello"
 
 
+def test_parse_content_list_with_single_string():
+    """Test _parse_content_list treats a bare string as one text item, not one per character."""
+    result = _parse_content_list("hello")
+
+    assert len(result) == 1
+    assert result[0].type == "text"
+    assert result[0].text == "hello"
+
+
 def test_parse_content_list_with_mixed_content_and_dict():
     """Test _parse_content_list handles a mix of Content objects and dicts."""
     content = Content(type="text", text="hello")