- Issue #6939: Fix file I/O objects in the `io` module to keep the original
file position when calling `truncate()`. It would previously change the
file position to the given argument, which goes against the tradition of
ftruncate() and other truncation APIs. Patch by Pascal Chambon.
diff --git a/Lib/test/test_io.py b/Lib/test/test_io.py
index 6f136f2..b91c0a1 100644
--- a/Lib/test/test_io.py
+++ b/Lib/test/test_io.py
@@ -234,6 +234,11 @@
def write_ops(self, f):
self.assertEqual(f.write(b"blah."), 5)
+ f.truncate(0)
+ self.assertEqual(f.tell(), 5)
+ f.seek(0)
+
+ self.assertEqual(f.write(b"blah."), 5)
self.assertEqual(f.seek(0), 0)
self.assertEqual(f.write(b"Hello."), 6)
self.assertEqual(f.tell(), 6)
@@ -244,8 +249,9 @@
self.assertEqual(f.write(b"h"), 1)
self.assertEqual(f.seek(-1, 2), 13)
self.assertEqual(f.tell(), 13)
+
self.assertEqual(f.truncate(12), 12)
- self.assertEqual(f.tell(), 12)
+ self.assertEqual(f.tell(), 13)
self.assertRaises(TypeError, f.seek, 0.0)
def read_ops(self, f, buffered=False):
@@ -290,7 +296,7 @@
self.assertEqual(f.tell(), self.LARGE + 2)
self.assertEqual(f.seek(0, 2), self.LARGE + 2)
self.assertEqual(f.truncate(self.LARGE + 1), self.LARGE + 1)
- self.assertEqual(f.tell(), self.LARGE + 1)
+ self.assertEqual(f.tell(), self.LARGE + 2)
self.assertEqual(f.seek(0, 2), self.LARGE + 1)
self.assertEqual(f.seek(-1, 2), self.LARGE)
self.assertEqual(f.read(2), b"x")
@@ -988,7 +994,7 @@
bufio = self.tp(raw, 8)
bufio.write(b"abcdef")
self.assertEqual(bufio.truncate(3), 3)
- self.assertEqual(bufio.tell(), 3)
+ self.assertEqual(bufio.tell(), 6)
with self.open(support.TESTFN, "rb", buffering=0) as f:
self.assertEqual(f.read(), b"abc")
@@ -1374,6 +1380,14 @@
self.assertEqual(s,
b"A" + b"B" * overwrite_size + b"A" * (9 - overwrite_size))
+ def test_truncate_after_read_or_write(self):
+ raw = self.BytesIO(b"A" * 10)
+ bufio = self.tp(raw, 100)
+ self.assertEqual(bufio.read(2), b"AA") # the read buffer gets filled
+ self.assertEqual(bufio.truncate(), 2)
+ self.assertEqual(bufio.write(b"BB"), 2) # the write buffer increases
+ self.assertEqual(bufio.truncate(), 4)
+
def test_misbehaved_io(self):
BufferedReaderTest.test_misbehaved_io(self)
BufferedWriterTest.test_misbehaved_io(self)