From 4b3a2f543276af1fad377205fe20332f3d71398c Mon Sep 17 00:00:00 2001
From: Colin Maudry <colin@maudry.com>
Date: Thu, 9 Jul 2026 19:53:08 +0200
Subject: [PATCH] =?UTF-8?q?feat(mcp):=20s=C3=A9rialisation=20Polars=20->?=
 =?UTF-8?q?=20JSON=20pour=20les=20tools=20MCP?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
---
 src/mcp/__init__.py             |  0
 src/mcp/serialization.py        | 21 +++++++++++++++++++++
 tests/mcp/__init__.py           |  0
 tests/mcp/test_serialization.py | 20 ++++++++++++++++++++
 4 files changed, 41 insertions(+)
 create mode 100644 src/mcp/__init__.py
 create mode 100644 src/mcp/serialization.py
 create mode 100644 tests/mcp/__init__.py
 create mode 100644 tests/mcp/test_serialization.py

diff --git a/src/mcp/__init__.py b/src/mcp/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/mcp/serialization.py b/src/mcp/serialization.py
new file mode 100644
index 0000000..9b81ff5
--- /dev/null
+++ b/src/mcp/serialization.py
@@ -0,0 +1,21 @@
+import datetime
+from typing import Any
+
+import polars as pl
+
+
+def to_json_records(df: pl.DataFrame) -> list[dict[str, Any]]:
+    """Convertit un DataFrame Polars en liste de dicts JSON-sérialisables.
+
+    Les dates/datetimes deviennent des chaînes ISO 8601 ; les valeurs nulles
+    restent None. Utilisé par tous les tools MCP pour produire une sortie propre.
+    """
+    return [
+        {key: _jsonify(value) for key, value in row.items()} for row in df.to_dicts()
+    ]
+
+
+def _jsonify(value: Any) -> Any:
+    if isinstance(value, (datetime.date, datetime.datetime)):
+        return value.isoformat()
+    return value
diff --git a/tests/mcp/__init__.py b/tests/mcp/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/mcp/test_serialization.py b/tests/mcp/test_serialization.py
new file mode 100644
index 0000000..ad35b88
--- /dev/null
+++ b/tests/mcp/test_serialization.py
@@ -0,0 +1,20 @@
+import datetime
+
+import polars as pl
+
+from src.mcp.serialization import to_json_records
+
+
+def test_dates_become_iso_strings():
+    df = pl.DataFrame({"d": [datetime.date(2025, 1, 1)], "n": [10]})
+    assert to_json_records(df) == [{"d": "2025-01-01", "n": 10}]
+
+
+def test_none_is_preserved():
+    df = pl.DataFrame({"nom": [None], "x": [3]})
+    assert to_json_records(df) == [{"nom": None, "x": 3}]
+
+
+def test_strings_and_numbers_untouched():
+    df = pl.DataFrame({"s": ["abc"], "f": [1.5]})
+    assert to_json_records(df) == [{"s": "abc", "f": 1.5}]