pbo-45593: make SpooledTemporaryFile.truncate return new file size

Author: rooterkyberian

Doc/library/tempfile.rst

@@ -172,6 +172,9 @@ The module defines the following user-callable items:
       :class:`io.TextIOBase` abstract base classes (depending on whether binary
       or text *mode* was specified).
 
+   .. versionchanged:: 3.12
+      The truncate method returns new file size.
+
 
 .. class:: TemporaryDirectory(suffix=None, prefix=None, dir=None, ignore_cleanup_errors=False, *, delete=True)
 
@@ -388,6 +391,7 @@ Here are some examples of typical usage of the :mod:`tempfile` module::
     >>> fp.write(b'Hello world!')
     # read data from file
     >>> fp.seek(0)
+    0
     >>> fp.read()
     b'Hello world!'
     # close the file, it will be removed

Lib/test/test_tempfile.py

@@ -1470,6 +1470,19 @@ def test_truncate_with_size_parameter(self):
         self.assertTrue(f._rolled)
         self.assertEqual(os.fstat(f.fileno()).st_size, 20)
 
+    def test_truncate_return_size(self):
+        "SpooledTemporaryFile truncate should return new position"
+        f = tempfile.SpooledTemporaryFile(max_size=10)
+        f.write(b'abcdef')
+        self.assertEqual(f.truncate(3), 3)
+
+    def test_seek_return_position(self):
+        "SpooledTemporaryFile seek should return file position"
+        f = tempfile.SpooledTemporaryFile(max_size=10)
+        f.write(b'abcdef')
+        self.assertEqual(f.seek(3), 3)
+        self.assertEqual(f.seek(0, 2), 6)
+
     def test_class_getitem(self):
         self.assertIsInstance(tempfile.SpooledTemporaryFile[bytes],
                       types.GenericAlias)

Misc/NEWS.d/next/Library/2021-10-24-01-28-07.bpo-45593.QjC6-D.rst

@@ -0,0 +1 @@
+Make :meth:`tempfile.SpooledTemporaryFile.truncate()` to return new file size.