Add date_part() BQL function

beanquery/query_env.py

@@ -592,6 +592,36 @@ def date_trunc(field, x):
     return None
 
 
+@function([str, datetime.date], int)
+def date_part(field, x):
+    """Extract the specified field from a date."""
+    if field == 'weekday' or field == 'dow':
+        return x.weekday()
+    if field == 'isoweekday' or field == 'isodow':
+        return x.isoweekday()
+    if field == 'week':
+        # isocalendar() returns a named tuple only in Python >= 3.9.
+        return x.isocalendar()[1]
+    if field == 'month':
+        return x.month
+    if field == 'quarter':
+        return (x.month - 1) // 3 + 1
+    if field == 'year':
+        return x.year
+    if field == 'isoyear':
+        # isocalendar() returns a named tuple only in Python >= 3.9.
+        return x.isocalendar()[0]
+    if field == 'decade':
+        return x.year // 10
+    if field == 'century':
+        return (x.year - 1) // 100 + 1
+    if field == 'millennium':
+        return (x.year - 1) // 1000 + 1
+    if field == 'epoch':
+        return int((x - datetime.date(1970, 1, 1)).total_seconds())
+    return None
+
+
 @function([str], relativedelta)
 def interval(x):
     """Construct a relative time interval."""

beanquery/query_env_test.py

@@ -206,6 +206,22 @@ def assertResult(self, expr, result):
             columns, rows = query.run_query([], {}, f'SELECT {expr} FROM #')
             self.assertEqual(rows[0][0], result)
 
+    def test_date_part(self):
+        self.assertResult('date_part("weekday", 2024-06-09)', 6)
+        self.assertResult('date_part("dow", 2024-06-09)', 6)
+        self.assertResult('date_part("isoweekday", 2024-06-09)', 7)
+        self.assertResult('date_part("isodow", 2024-06-09)', 7)
+        self.assertResult('date_part("week", 2024-06-09)', 23)
+        self.assertResult('date_part("month", 2024-06-09)', 6)
+        self.assertResult('date_part("quarter", 2024-06-09)', 2)
+        self.assertResult('date_part("year", 2024-06-09)', 2024)
+        self.assertResult('date_part("isoyear", 2024-06-09)', 2024)
+        self.assertResult('date_part("decade", 2024-06-09)', 202)
+        self.assertResult('date_part("century", 2024-06-09)', 21)
+        self.assertResult('date_part("millennium", 2024-06-09)', 3)
+        self.assertResult('date_part("epoch", 2024-06-09)', 1717891200)
+        self.assertResult('date_part("baz", 2024-06-09)', None)
+
     def test_date_trunc(self):
         self.assertResult('date_trunc("week", 2016-11-14)', datetime.date(2016, 11, 14)) # monday
         self.assertResult('date_trunc("week", 2016-11-15)', datetime.date(2016, 11, 14)) # tuesday

pyproject.toml

@@ -71,6 +71,7 @@ ignore = [
     'PLR0912',
     'PLR0913',
     'PLR0915',
+    'PLR1714',
     'PLR2004',
     'PLW2901',
     'RUF012',