Fix to_sharegpt optional block rendering "None" for missing extra columns

tests/python/test_to_sharegpt_optional_none.py

@@ -0,0 +1,75 @@
+import ast
+import re
+from pathlib import Path
+
+
+def _load_formatter_builders():
+    # Extract _parse_combined_prompt and _create_formatter without importing
+    # unsloth (importing unsloth needs unsloth_zoo / a GPU). Both are pure
+    # Python and only use the `re` module.
+    source = Path(__file__).parents[2] / "unsloth" / "chat_templates.py"
+    tree = ast.parse(source.read_text(encoding = "utf-8"))
+    wanted = {"_parse_combined_prompt", "_create_formatter"}
+    funcs = [
+        node for node in tree.body if isinstance(node, ast.FunctionDef) and node.name in wanted
+    ]
+    namespace = {"re": re}
+    module = ast.Module(body = funcs, type_ignores = [])
+    ast.fix_missing_locations(module)
+    exec(compile(module, str(source), "exec"), namespace)
+    return namespace["_parse_combined_prompt"], namespace["_create_formatter"]
+
+
+class _StubDataset:
+    def __init__(self, column_names):
+        self.column_names = column_names
+
+
+def _render(merged_prompt, columns, batch):
+    parse, create = _load_formatter_builders()
+    possible_columns, final_optional_prompts = parse(merged_prompt, _StubDataset(columns))
+    processor = create(possible_columns, final_optional_prompts, "text")
+    return processor(batch)["text"]
+
+
+def test_optional_block_missing_second_column_does_not_render_none():
+    # A [[...]] block may reference several columns; only the first gates the
+    # block. A later column that is None must not render as the literal "None".
+    merged_prompt = "Location: [[{city}, {country}]] end"
+    out = _render(
+        merged_prompt,
+        ["city", "country"],
+        {"city": ["Paris"], "country": [None]},
+    )
+    assert out[0] == "Location: Paris,  end"
+    assert "None" not in out[0]
+
+
+def test_optional_block_all_columns_present_unchanged():
+    merged_prompt = "Location: [[{city}, {country}]] end"
+    out = _render(
+        merged_prompt,
+        ["city", "country"],
+        {"city": ["Paris"], "country": ["France"]},
+    )
+    assert out[0] == "Location: Paris, France end"
+
+
+def test_optional_block_gating_column_empty_is_dropped():
+    # When the gating (first) column is empty the whole block is omitted; this
+    # behaviour is unchanged by the None coercion.
+    merged_prompt = "Location: [[{city}, {country}]] end"
+    out = _render(
+        merged_prompt,
+        ["city", "country"],
+        {"city": [""], "country": ["France"]},
+    )
+    assert out[0] == "Location:  end"
+
+
+def test_single_column_optional_block_gated_out_on_none():
+    # Single-column blocks were already gated correctly (the sole column is the
+    # gate); confirm they stay unaffected.
+    merged_prompt = "Name: [[{name}]]!"
+    out = _render(merged_prompt, ["name"], {"name": [None, "Bob"]})
+    assert out == ["Name: !", "Name: Bob!"]

unsloth/chat_templates.py

@@ -2163,7 +2163,14 @@ def __combined_prompt_processor__(examples):
 
                 _, optional_name, prompt, needed_columns = formatter_template
                 if row_values[needed_columns[0]] not in (None, ""):
-                    prompt_values = {column: row_values[column] for column in needed_columns}
+                    # Coerce missing (None) columns to "" so they do not render as the
+                    # literal string "None" in the emitted text. A [[...]] block may
+                    # reference several columns; only the first gates the block, so a
+                    # later column can still be None here.
+                    prompt_values = {
+                        column: ("" if row_values[column] is None else row_values[column])
+                        for column in needed_columns
+                    }
                     formatter_values[optional_name] = prompt.format(**prompt_values)
                 else:
                     formatter_values[optional_name] = ""