table.default_values property, closes #475

Refs #468

Author: simonw

docs/python-api.rst

@@ -1802,6 +1802,16 @@ The ``.columns_dict`` property returns a dictionary version of the columns with
     >>> db["PlantType"].columns_dict
     {'id': <class 'int'>, 'value': <class 'str'>}
 
+.. _python_api_introspection_default_values:
+
+.default_values
+---------------
+
+The ``.default_values`` property returns a dictionary of default values for each column that has a default::
+
+    >>> db["table_with_defaults"].default_values
+    {'score': 5}
+
 .. _python_api_introspection_pks:
 
 .pks

sqlite_utils/db.py

@@ -9,6 +9,7 @@
     progressbar,
     find_spatialite,
 )
+import binascii
 from collections import namedtuple
 from collections.abc import Mapping
 import contextlib
@@ -1458,6 +1459,15 @@ def triggers_dict(self) -> Dict[str, str]:
         "``{trigger_name: sql}`` dictionary of triggers defined on this table."
         return {trigger.name: trigger.sql for trigger in self.triggers}
 
+    @property
+    def default_values(self) -> Dict[str, Any]:
+        "``{column_name: default_value}`` dictionary of default values for columns in this table."
+        return {
+            column.name: _decode_default_value(column.default_value)
+            for column in self.columns
+            if column.default_value is not None
+        }
+
     @property
     def strict(self) -> bool:
         "Is this a STRICT table?"
@@ -3527,3 +3537,22 @@ def fix_square_braces(records: Iterable[Dict[str, Any]]):
             }
         else:
             yield record
+
+
+def _decode_default_value(value):
+    if value.startswith("'") and value.endswith("'"):
+        # It's a string
+        return value[1:-1]
+    if value.isdigit():
+        # It's an integer
+        return int(value)
+    if value.startswith("X'") and value.endswith("'"):
+        # It's a binary string, stored as hex
+        to_decode = value[2:-1]
+        return binascii.unhexlify(to_decode)
+    # If it is a string containing a floating point number:
+    try:
+        return float(value)
+    except ValueError:
+        pass
+    return value

tests/test_introspect.py

@@ -299,3 +299,21 @@ def test_table_strict(fresh_db, create_table, expected_strict):
     fresh_db.execute(create_table)
     table = fresh_db["t"]
     assert table.strict == expected_strict
+
+
+@pytest.mark.parametrize(
+    "value",
+    (
+        1,
+        1.3,
+        "foo",
+        True,
+        b"binary",
+    ),
+)
+def test_table_default_values(fresh_db, value):
+    fresh_db["default_values"].insert(
+        {"nodefault": 1, "value": value}, defaults={"value": value}
+    )
+    default_values = fresh_db["default_values"].default_values
+    assert default_values == {"value": value}