(Merge 3.6) Issue #23840: tokenize.open() now closes the temporary binary file

on error to fix a resource warning.

Lib/test/test_tokenize.py

@@ -834,7 +834,7 @@ from tokenize import (tokenize, _tokenize, untokenize, NUMBER, NAME, OP,
                      STRING, ENDMARKER, ENCODING, tok_name, detect_encoding,
                      open as tokenize_open, Untokenizer)
 from io import BytesIO
-from unittest import TestCase
+from unittest import TestCase, mock
 import os, sys, glob
 import token
 
@@ -1246,6 +1246,14 @@ class TestDetectEncoding(TestCase):
             ins = Bunk(lines, path)
             detect_encoding(ins.readline)
 
+    def test_open_error(self):
+        # Issue #23840: open() must close the binary file on error
+        m = BytesIO(b'#coding:xxx')
+        with mock.patch('tokenize._builtin_open', return_value=m):
+            self.assertRaises(SyntaxError, tokenize_open, 'foobar')
+        self.assertTrue(m.closed)
+
+
 
 class TestTokenize(TestCase):
 

Lib/tokenize.py

@@ -435,11 +435,15 @@ def open(filename):
     detect_encoding().
     """
     buffer = _builtin_open(filename, 'rb')
+    try:
         encoding, lines = detect_encoding(buffer.readline)
         buffer.seek(0)
         text = TextIOWrapper(buffer, encoding, line_buffering=True)
         text.mode = 'r'
         return text
+    except:
+        buffer.close()
+        raise
 
 
 def tokenize(readline):

Misc/NEWS

@@ -335,6 +335,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #23840: tokenize.open() now closes the temporary binary file on error
+  to fix a resource warning.
+
 - Issue #16914: new debuglevel 2 in smtplib adds timestamps to debug output.
 
 - Issue #7159: urllib.request now supports sending auth credentials