gh-69093: Add context manager support to sqlite3.Blob

python · JelleZijlstra · Apr 16, 2022 · Apr 13, 2022 · Apr 15, 2022 · Apr 15, 2022
commit b6cd651ef489ed012479740f96076638fc25d9f1
diff --git a/Doc/includes/sqlite3/blob_with.py b/Doc/includes/sqlite3/blob_with.py
@@ -0,0 +1,12 @@
+import sqlite3
+
+con = sqlite3.connect(":memory:")
+
+con.execute("create table test(blob_col blob)")
+con.execute("insert into test(blob_col) values (zeroblob(10))")
+
+with con.blobopen("test", "blob_col", 1) as blob:
+    blob.write(b"Hello")
+    blob.write(b"World")
+    blob.seek(0)
+    print(blob.read())  # will print b"HelloWorld"
@@ -1153,6 +1153,10 @@ Blob Objects
 
       .. literalinclude:: ../includes/sqlite3/blob.py
 
+   A :class:`Blob` can also be used as a :term:`context manager`:
+
+      .. literalinclude:: ../includes/sqlite3/blob_with.py
+
 
 .. _sqlite3-types:
 

@@ -1166,6 +1166,25 @@ def test_blob_sequence_not_supported(self):
         with self.assertRaises(TypeError):
             b"a" in self.blob
 
+    def test_blob_context_manager(self):
+        data = b"a" * 50
+        with self.cx.blobopen("test", "b", 1) as blob:
+            blob.write(data)
+        actual = self.cx.execute("select b from test").fetchone()[0]
+        self.assertEqual(actual, data)
+
+        # Check that __exit__ closed the blob
+        with self.assertRaisesRegex(sqlite.ProgrammingError, "closed blob"):
+            blob.read()
+
+    def test_blob_context_manager_reraise_exceptions(self):
+        class DummyException(Exception):
+            pass
+        with self.assertRaisesRegex(DummyException, "reraised"):
+            with self.cx.blobopen("test", "b", 1) as blob:
+                raise DummyException("reraised")
+
+
     def test_blob_closed(self):
         with memory_database() as cx:
             cx.execute("create table test(b blob)")
@@ -1182,6 +1201,10 @@ def test_blob_closed(self):
                 blob.seek(0)
             with self.assertRaisesRegex(sqlite.ProgrammingError, msg):
                 blob.tell()
+            with self.assertRaisesRegex(sqlite.ProgrammingError, msg):
+                blob.__enter__()
+            with self.assertRaisesRegex(sqlite.ProgrammingError, msg):
+                blob.__exit__(None, None, None)
 
     def test_blob_closed_db_read(self):
         with memory_database() as cx:

diff --git a/Misc/NEWS.d/next/Library/2022-04-14-00-59-01.gh-issue-69093.bmlMwI.rst b/Misc/NEWS.d/next/Library/2022-04-14-00-59-01.gh-issue-69093.bmlMwI.rst
@@ -0,0 +1,2 @@
+Add :term:`context manager` support to :class:`sqlite3.Blob`.
+Patch by Aviv Palivoda and Erlend E. Aasland.
@@ -307,8 +307,51 @@ blob_tell_impl(pysqlite_Blob *self)
 }
 
 
+/*[clinic input]
+_sqlite3.Blob.__enter__ as blob_enter
+
+Blob context manager enter.
+[clinic start generated code]*/
+
+static PyObject *
+blob_enter_impl(pysqlite_Blob *self)
+/*[clinic end generated code: output=4fd32484b071a6cd input=fe4842c3c582d5a7]*/
+{
+    if (!check_blob(self)) {
+        return NULL;
+    }
+    return Py_NewRef(self);
+}
+
+
+/*[clinic input]
+_sqlite3.Blob.__exit__ as blob_exit
+
+    type: object
+    val: object
+    tb: object
+    /
+
+Blob context manager exit.
+[clinic start generated code]*/
+
+static PyObject *
+blob_exit_impl(pysqlite_Blob *self, PyObject *type, PyObject *val,
+               PyObject *tb)
+/*[clinic end generated code: output=fc86ceeb2b68c7b2 input=575d9ecea205f35f]*/
+{
+    if (!check_blob(self)) {
+        return NULL;
+    }
+    close_blob(self);
+    Py_RETURN_FALSE;
+}
+
+
 static PyMethodDef blob_methods[] = {
     BLOB_CLOSE_METHODDEF
+    BLOB_ENTER_METHODDEF
+    BLOB_EXIT_METHODDEF
     BLOB_READ_METHODDEF
     BLOB_SEEK_METHODDEF
     BLOB_TELL_METHODDEF
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Add :term:`context manager` support to :class:`sqlite3.Blob`.
		Patch by Aviv Palivoda and Erlend E. Aasland.