gh-79097: Add support for aggregate window functions in sqlite3 (GH-20903)

Author: Erlend Egeberg Aasland

Doc/includes/sqlite3/sumintwindow.py

@@ -0,0 +1,46 @@
+# Example taken from https://www.sqlite.org/windowfunctions.html#udfwinfunc
+import sqlite3
+
+
+class WindowSumInt:
+    def __init__(self):
+        self.count = 0
+
+    def step(self, value):
+        """Adds a row to the current window."""
+        self.count += value
+
+    def value(self):
+        """Returns the current value of the aggregate."""
+        return self.count
+
+    def inverse(self, value):
+        """Removes a row from the current window."""
+        self.count -= value
+
+    def finalize(self):
+        """Returns the final value of the aggregate.
+
+        Any clean-up actions should be placed here.
+        """
+        return self.count
+
+
+con = sqlite3.connect(":memory:")
+cur = con.execute("create table test(x, y)")
+values = [
+    ("a", 4),
+    ("b", 5),
+    ("c", 3),
+    ("d", 8),
+    ("e", 1),
+]
+cur.executemany("insert into test values(?, ?)", values)
+con.create_window_function("sumint", 1, WindowSumInt)
+cur.execute("""
+    select x, sumint(y) over (
+        order by x rows between 1 preceding and 1 following
+    ) as sum_y
+    from test order by x
+""")
+print(cur.fetchall())

Doc/library/sqlite3.rst

@@ -473,6 +473,35 @@ Connection Objects
       .. literalinclude:: ../includes/sqlite3/mysumaggr.py
 
 
+   .. method:: create_window_function(name, num_params, aggregate_class, /)
+
+      Creates user-defined aggregate window function *name*.
+
+      *aggregate_class* must implement the following methods:
+
+      * ``step``: adds a row to the current window
+      * ``value``: returns the current value of the aggregate
+      * ``inverse``: removes a row from the current window
+      * ``finalize``: returns the final value of the aggregate
+
+      ``step`` and ``value`` accept *num_params* number of parameters,
+      unless *num_params* is ``-1``, in which case they may take any number of
+      arguments.  ``finalize`` and ``value`` can return any of the types
+      supported by SQLite:
+      :class:`bytes`, :class:`str`, :class:`int`, :class:`float`, and
+      :const:`None`.  Call :meth:`create_window_function` with
+      *aggregate_class* set to :const:`None` to clear window function *name*.
+
+      Aggregate window functions are supported by SQLite 3.25.0 and higher.
+      :exc:`NotSupportedError` will be raised if used with older versions.
+
+      .. versionadded:: 3.11
+
+      Example:
+
+      .. literalinclude:: ../includes/sqlite3/sumintwindow.py
+
+
    .. method:: create_collation(name, callable)
 
       Creates a collation with the specified *name* and *callable*. The callable will

Doc/whatsnew/3.11.rst

@@ -389,6 +389,10 @@ sqlite3
   serializing and deserializing databases.
   (Contributed by Erlend E. Aasland in :issue:`41930`.)
 
+* Add :meth:`~sqlite3.Connection.create_window_function` to
+  :class:`sqlite3.Connection` for creating aggregate window functions.
+  (Contributed by Erlend E. Aasland in :issue:`34916`.)
+
 
 sys
 ---

Lib/test/test_sqlite3/test_dbapi.py

@@ -1084,6 +1084,8 @@ def test_check_connection_thread(self):
         if hasattr(sqlite.Connection, "serialize"):
             fns.append(lambda: self.con.serialize())
             fns.append(lambda: self.con.deserialize(b""))
+        if sqlite.sqlite_version_info >= (3, 25, 0):
+            fns.append(lambda: self.con.create_window_function("foo", 0, None))
 
         for fn in fns:
             with self.subTest(fn=fn):

Lib/test/test_sqlite3/test_userfunctions.py

@@ -27,9 +27,9 @@
 import re
 import sys
 import unittest
-import unittest.mock
 import sqlite3 as sqlite
 
+from unittest.mock import Mock, patch
 from test.support import bigmemtest, catch_unraisable_exception, gc_collect
 
 from test.test_sqlite3.test_dbapi import cx_limit
@@ -393,7 +393,7 @@ def append_result(arg):
     # indices, which allows testing based on syntax, iso. the query optimizer.
     @unittest.skipIf(sqlite.sqlite_version_info < (3, 8, 3), "Requires SQLite 3.8.3 or higher")
     def test_func_non_deterministic(self):
-        mock = unittest.mock.Mock(return_value=None)
+        mock = Mock(return_value=None)
         self.con.create_function("nondeterministic", 0, mock, deterministic=False)
         if sqlite.sqlite_version_info < (3, 15, 0):
             self.con.execute("select nondeterministic() = nondeterministic()")
@@ -404,7 +404,7 @@ def test_func_non_deterministic(self):
 
     @unittest.skipIf(sqlite.sqlite_version_info < (3, 8, 3), "Requires SQLite 3.8.3 or higher")
     def test_func_deterministic(self):
-        mock = unittest.mock.Mock(return_value=None)
+        mock = Mock(return_value=None)
         self.con.create_function("deterministic", 0, mock, deterministic=True)
         if sqlite.sqlite_version_info < (3, 15, 0):
             self.con.execute("select deterministic() = deterministic()")
@@ -482,6 +482,164 @@ def test_func_return_illegal_value(self):
                                self.con.execute, "select badreturn()")
 
 
+class WindowSumInt:
+    def __init__(self):
+        self.count = 0
+
+    def step(self, value):
+        self.count += value
+
+    def value(self):
+        return self.count
+
+    def inverse(self, value):
+        self.count -= value
+
+    def finalize(self):
+        return self.count
+
+class BadWindow(Exception):
+    pass
+
+
+@unittest.skipIf(sqlite.sqlite_version_info < (3, 25, 0),
+                 "Requires SQLite 3.25.0 or newer")
+class WindowFunctionTests(unittest.TestCase):
+    def setUp(self):
+        self.con = sqlite.connect(":memory:")
+        self.cur = self.con.cursor()
+
+        # Test case taken from https://www.sqlite.org/windowfunctions.html#udfwinfunc
+        values = [
+            ("a", 4),
+            ("b", 5),
+            ("c", 3),
+            ("d", 8),
+            ("e", 1),
+        ]
+        with self.con:
+            self.con.execute("create table test(x, y)")
+            self.con.executemany("insert into test values(?, ?)", values)
+        self.expected = [
+            ("a", 9),
+            ("b", 12),
+            ("c", 16),
+            ("d", 12),
+            ("e", 9),
+        ]
+        self.query = """
+            select x, %s(y) over (
+                order by x rows between 1 preceding and 1 following
+            ) as sum_y
+            from test order by x
+        """
+        self.con.create_window_function("sumint", 1, WindowSumInt)
+
+    def test_win_sum_int(self):
+        self.cur.execute(self.query % "sumint")
+        self.assertEqual(self.cur.fetchall(), self.expected)
+
+    def test_win_error_on_create(self):
+        self.assertRaises(sqlite.ProgrammingError,
+                          self.con.create_window_function,
+                          "shouldfail", -100, WindowSumInt)
+
+    @with_tracebacks(BadWindow)
+    def test_win_exception_in_method(self):
+        for meth in "__init__", "step", "value", "inverse":
+            with self.subTest(meth=meth):
+                with patch.object(WindowSumInt, meth, side_effect=BadWindow):
+                    name = f"exc_{meth}"
+                    self.con.create_window_function(name, 1, WindowSumInt)
+                    msg = f"'{meth}' method raised error"
+                    with self.assertRaisesRegex(sqlite.OperationalError, msg):
+                        self.cur.execute(self.query % name)
+                        self.cur.fetchall()
+
+    @with_tracebacks(BadWindow)
+    def test_win_exception_in_finalize(self):
+        # Note: SQLite does not (as of version 3.38.0) propagate finalize
+        # callback errors to sqlite3_step(); this implies that OperationalError
+        # is _not_ raised.
+        with patch.object(WindowSumInt, "finalize", side_effect=BadWindow):
+            name = f"exception_in_finalize"
+            self.con.create_window_function(name, 1, WindowSumInt)
+            self.cur.execute(self.query % name)
+            self.cur.fetchall()
+
+    @with_tracebacks(AttributeError)
+    def test_win_missing_method(self):
+        class MissingValue:
+            def step(self, x): pass
+            def inverse(self, x): pass
+            def finalize(self): return 42
+
+        class MissingInverse:
+            def step(self, x): pass
+            def value(self): return 42
+            def finalize(self): return 42
+
+        class MissingStep:
+            def value(self): return 42
+            def inverse(self, x): pass
+            def finalize(self): return 42
+
+        dataset = (
+            ("step", MissingStep),
+            ("value", MissingValue),
+            ("inverse", MissingInverse),
+        )
+        for meth, cls in dataset:
+            with self.subTest(meth=meth, cls=cls):
+                name = f"exc_{meth}"
+                self.con.create_window_function(name, 1, cls)
+                with self.assertRaisesRegex(sqlite.OperationalError,
+                                            f"'{meth}' method not defined"):
+                    self.cur.execute(self.query % name)
+                    self.cur.fetchall()
+
+    @with_tracebacks(AttributeError)
+    def test_win_missing_finalize(self):
+        # Note: SQLite does not (as of version 3.38.0) propagate finalize
+        # callback errors to sqlite3_step(); this implies that OperationalError
+        # is _not_ raised.
+        class MissingFinalize:
+            def step(self, x): pass
+            def value(self): return 42
+            def inverse(self, x): pass
+
+        name = "missing_finalize"
+        self.con.create_window_function(name, 1, MissingFinalize)
+        self.cur.execute(self.query % name)
+        self.cur.fetchall()
+
+    def test_win_clear_function(self):
+        self.con.create_window_function("sumint", 1, None)
+        self.assertRaises(sqlite.OperationalError, self.cur.execute,
+                          self.query % "sumint")
+
+    def test_win_redefine_function(self):
+        # Redefine WindowSumInt; adjust the expected results accordingly.
+        class Redefined(WindowSumInt):
+            def step(self, value): self.count += value * 2
+            def inverse(self, value): self.count -= value * 2
+        expected = [(v[0], v[1]*2) for v in self.expected]
+
+        self.con.create_window_function("sumint", 1, Redefined)
+        self.cur.execute(self.query % "sumint")
+        self.assertEqual(self.cur.fetchall(), expected)
+
+    def test_win_error_value_return(self):
+        class ErrorValueReturn:
+            def __init__(self): pass
+            def step(self, x): pass
+            def value(self): return 1 << 65
+
+        self.con.create_window_function("err_val_ret", 1, ErrorValueReturn)
+        self.assertRaisesRegex(sqlite.DataError, "string or blob too big",
+                               self.cur.execute, self.query % "err_val_ret")
+
+
 class AggregateTests(unittest.TestCase):
     def setUp(self):
         self.con = sqlite.connect(":memory:")
@@ -527,10 +685,10 @@ def test_aggr_no_step(self):
 
     def test_aggr_no_finalize(self):
         cur = self.con.cursor()
-        with self.assertRaises(sqlite.OperationalError) as cm:
+        msg = "user-defined aggregate's 'finalize' method not defined"
+        with self.assertRaisesRegex(sqlite.OperationalError, msg):
             cur.execute("select nofinalize(t) from test")
             val = cur.fetchone()[0]
-        self.assertEqual(str(cm.exception), "user-defined aggregate's 'finalize' method raised error")
 
     @with_tracebacks(ZeroDivisionError, name="AggrExceptionInInit")
     def test_aggr_exception_in_init(self):

Misc/NEWS.d/next/Library/2020-05-24-23-52-03.bpo-40617.lycF9q.rst

@@ -0,0 +1,3 @@
+Add :meth:`~sqlite3.Connection.create_window_function` to
+:class:`sqlite3.Connection` for creating aggregate window functions.
+Patch by Erlend E. Aasland.