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.

1 files changed, 3 insertions, 5 deletions

diff --git a/Lib/io.py b/Lib/io.py
index 70f2aba..d090eec 100644
--- a/Lib/io.py
+++ b/Lib/io.py
@@ -880,7 +880,7 @@ class _BytesIO(BufferedIOBase):
         elif pos < 0:
             raise ValueError("negative truncate position %r" % (pos,))
         del self._buffer[pos:]
-        return self.seek(pos)
+        return pos
 
     def readable(self):
         return True
@@ -1215,8 +1215,7 @@ class BufferedRandom(BufferedWriter, BufferedReader):
         if pos is None:
             pos = self.tell()
         # Use seek to flush the read buffer.
-        self.seek(pos)
-        return BufferedWriter.truncate(self)
+        return BufferedWriter.truncate(self, pos)
 
     def read(self, n=None):
         if n is None:
@@ -1667,8 +1666,7 @@ class TextIOWrapper(TextIOBase):
         self.flush()
         if pos is None:
             pos = self.tell()
-        self.seek(pos)
-        return self.buffer.truncate()
+        return self.buffer.truncate(pos)
 
     def seek(self, cookie, whence=0):
         if self.closed: