Backport bug #1194181: bz2.BZ2File didn't handle mode 'U' correctly.

Lib/test/test_bz2.py

@@ -235,6 +235,16 @@ class BZ2FileTest(BaseTest):
         # "Test opening a nonexistent file"
         self.assertRaises(IOError, BZ2File, "/non/existent")
 
+    def testModeU(self):
+        # Bug #1194181: bz2.BZ2File opened for write with mode "U"
+        self.createTempFile()
+        bz2f = BZ2File(self.filename, "U")
+        bz2f.close()
+        f = file(self.filename)
+        f.seek(0, 2)
+        self.assertEqual(f.tell(), len(self.DATA))
+        f.close()
+
 class BZ2CompressorTest(BaseTest):
     def testCompress(self):
         # "Test BZ2Compressor.compress()/flush()"

Misc/NEWS

@@ -27,6 +27,8 @@ Core and builtins
 Extension Modules
 -----------------
 
+- Bug #1194181: bz2.BZ2File didn't handle mode 'U' correctly.
+
 - Bug #1166660: The readline module could segfault if hook functions
   were set in a different thread than that which called readline.
 

Modules/bz2module.c

@@ -1308,6 +1308,10 @@ BZ2File_init(BZ2FileObject *self, PyObject *args, PyObject *kwargs)
 			break;
 	}
 
+	if (mode_char == 0) {
+		mode_char = 'r';
+	}
+
 	mode = (mode_char == 'r') ? "rb" : "wb";
 
 	self->file = PyObject_CallFunction((PyObject*)&PyFile_Type, "(Osi)",