Bug #1548891: The cStringIO.StringIO() constructor now encodes unicode

arguments with the system default encoding just like the write()
method does, instead of converting it to a raw buffer.
 (backport from rev. 52301)

Lib/test/test_StringIO.py

@@ -120,6 +120,28 @@ class TestStringIO(TestGenericStringIO):
 class TestcStringIO(TestGenericStringIO):
     MODULE = cStringIO
 
+    def test_unicode(self):
+
+        if not test_support.have_unicode: return
+
+        # The cStringIO module converts Unicode strings to character
+        # strings when writing them to cStringIO objects.
+        # Check that this works.
+
+        f = self.MODULE.StringIO()
+        f.write(unicode(self._line[:5]))
+        s = f.getvalue()
+        self.assertEqual(s, 'abcde')
+        self.assertEqual(type(s), types.StringType)
+
+        f = self.MODULE.StringIO(unicode(self._line[:5]))
+        s = f.getvalue()
+        self.assertEqual(s, 'abcde')
+        self.assertEqual(type(s), types.StringType)
+
+        self.assertRaises(UnicodeEncodeError, self.MODULE.StringIO,
+                          unicode('\xf4', 'latin-1'))
+
 import sys
 if sys.platform.startswith('java'):
     # Jython doesn't have a buffer object, so we just do a useless

Misc/NEWS

@@ -49,6 +49,10 @@ Core and builtins
 Extension Modules
 -----------------
 
+- Bug #1548891: The cStringIO.StringIO() constructor now encodes unicode
+  arguments with the system default encoding just like the write()
+  method does, instead of converting it to a raw buffer.
+
 - Bug #1565150: Fix subsecond processing for os.utime on Windows.
 
 - Patch #1572724: fix typo ('=' instead of '==') in _msi.c.

Modules/cStringIO.c

@@ -657,11 +657,9 @@ newIobject(PyObject *s) {
   char *buf;
   Py_ssize_t size;
 
-  if (PyObject_AsReadBuffer(s, (const void **)&buf, &size)) {
-      PyErr_Format(PyExc_TypeError, "expected read buffer, %.200s found",
-		   s->ob_type->tp_name);
+  if (PyObject_AsCharBuffer(s, (const void **)&buf, &size) != 0)
       return NULL;
-  }
+
   self = PyObject_New(Iobject, &Itype);
   if (!self) return NULL;
   Py_INCREF(s);