bpo-31291: Fixed an assertion failure in zipimport.zipimporter.get_data() (#3226)

if pathname.replace('/', '\\') returns non-string.

Lib/test/test_zipimport.py

@@ -521,6 +521,23 @@ class UncompressedZipImportTestCase(ImportHooksBaseTestCase):
             z.close()
             os.remove(TEMP_ZIP)
 
+    def test_issue31291(self):
+        # There shouldn't be an assertion failure in get_data().
+        class FunnyStr(str):
+            def replace(self, old, new):
+                return 42
+        z = ZipFile(TEMP_ZIP, "w")
+        try:
+            name = "test31291.dat"
+            data = b'foo'
+            z.writestr(name, data)
+            z.close()
+            zi = zipimport.zipimporter(TEMP_ZIP)
+            self.assertEqual(data, zi.get_data(FunnyStr(name)))
+        finally:
+            z.close()
+            os.remove(TEMP_ZIP)
+
     def testImporterAttr(self):
         src = """if 1:  # indent hack
         def get_file():

Misc/NEWS.d/next/Core and Builtins/2017-08-28-11-51-29.bpo-31291.t8QggK.rst

@@ -0,0 +1,3 @@
+Fix an assertion failure in `zipimport.zipimporter.get_data` on Windows,
+when the return value of ``pathname.replace('/','\\')`` isn't a string.
+Patch by Oren Milman.

Modules/zipimport.c

@@ -651,7 +651,8 @@ zipimport_zipimporter_get_data_impl(ZipImporter *self, PyObject *path)
     Py_ssize_t path_start, path_len, len;
 
 #ifdef ALTSEP
-    path = _PyObject_CallMethodId(path, &PyId_replace, "CC", ALTSEP, SEP);
+    path = _PyObject_CallMethodId((PyObject *)&PyUnicode_Type, &PyId_replace,
+                                  "OCC", path, ALTSEP, SEP);
     if (!path)
         return NULL;
 #else