bpo-37054, _pyio: Fix BytesIO and TextIOWrapper __del__() (GH-13601)

Fix destructor _pyio.BytesIO and _pyio.TextIOWrapper: initialize
their _buffer attribute as soon as possible (in the class body),
because it's used by __del__() which calls close().

1 files changed, 10 insertions, 1 deletions

diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 5baca4df82..43c24342ad 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -873,6 +873,10 @@ class BytesIO(BufferedIOBase):
 
     """Buffered I/O implementation using an in-memory bytes buffer."""
 
+    # Initialize _buffer as soon as possible since it's used by __del__()
+    # which calls close()
+    _buffer = None
+
     def __init__(self, initial_bytes=None):
         buf = bytearray()
         if initial_bytes is not None:
@@ -900,7 +904,8 @@ class BytesIO(BufferedIOBase):
         return memoryview(self._buffer)
 
     def close(self):
-        self._buffer.clear()
+        if self._buffer is not None:
+            self._buffer.clear()
         super().close()
 
     def read(self, size=-1):
@@ -1970,6 +1975,10 @@ class TextIOWrapper(TextIOBase):
 
     _CHUNK_SIZE = 2048
 
+    # Initialize _buffer as soon as possible since it's used by __del__()
+    # which calls close()
+    _buffer = None
+
     # The write_through argument has no effect here since this
     # implementation always writes through.  The argument is present only
     # so that the signature can match the signature of the C version.