bpo-40638: Check for attribute lookup failure in builtin_input_impl

Add tests to cover this case.

Lib/test/test_builtin.py

@@ -75,6 +75,23 @@ class BitBucket:
     def write(self, line):
         pass
 
+class MalformedInputStream:
+    def readline(self):
+        return "foobar\n"
+
+    def fileno(self):
+        return 0
+
+class MalformedOutputStream:
+    def __init__(self):
+        self.value = ""
+
+    def fileno(self):
+        return 1
+
+    def write(self, value):
+        self.value += value
+
 test_conv_no_sign = [
         ('0', 0),
         ('1', 1),
@@ -1302,6 +1319,13 @@ class BuiltinTest(unittest.TestCase):
             sys.stdin = io.StringIO()
             self.assertRaises(EOFError, input)
 
+            # input() in tty mode with a malformed input stream should attempt
+            # to call .readline()
+            sys.stdin = MalformedInputStream()
+            sys.stdout = MalformedOutputStream()
+            self.assertEqual(input("baz"), "foobar")  # strips \n
+            self.assertEqual(sys.stdout.value, "baz")
+
             del sys.stdout
             self.assertRaises(RuntimeError, input, 'prompt')
             del sys.stdin

Python/bltinmodule.c

@@ -2010,17 +2010,21 @@ builtin_input_impl(PyObject *module, PyObject *prompt)
 
         /* stdin is a text stream, so it must have an encoding. */
         stdin_encoding = _PyObject_GetAttrId(fin, &PyId_encoding);
+        if (!stdin_encoding || !PyUnicode_Check(stdin_encoding)) {
+            goto _readline_disable_tty_and_fall_back;
+        }
         stdin_errors = _PyObject_GetAttrId(fin, &PyId_errors);
-        if (!stdin_encoding || !stdin_errors ||
-                !PyUnicode_Check(stdin_encoding) ||
-                !PyUnicode_Check(stdin_errors)) {
-            tty = 0;
-            goto _readline_errors;
+        if (!stdin_errors || !PyUnicode_Check(stdin_errors)) {
+            goto _readline_disable_tty_and_fall_back;
         }
         stdin_encoding_str = PyUnicode_AsUTF8(stdin_encoding);
-        stdin_errors_str = PyUnicode_AsUTF8(stdin_errors);
-        if (!stdin_encoding_str || !stdin_errors_str)
+        if (!stdin_encoding_str) {
             goto _readline_errors;
+        }
+        stdin_errors_str = PyUnicode_AsUTF8(stdin_errors);
+        if (!stdin_errors_str) {
+            goto _readline_errors;
+        }
         tmp = _PyObject_CallMethodIdNoArgs(fout, &PyId_flush);
         if (tmp == NULL)
             PyErr_Clear();
@@ -2099,6 +2103,8 @@ builtin_input_impl(PyObject *module, PyObject *prompt)
 
         return result;
 
+    _readline_disable_tty_and_fall_back:
+        tty = 0;
     _readline_errors:
         Py_XDECREF(stdin_encoding);
         Py_XDECREF(stdout_encoding);