Fix TextIOWrapper assertion typo and simplify test

- Fix assertion to check skip_bytes instead of skip_back
- Use simpler test data b'line1\r' instead of b'line1=1\r'
- Remove unnecessary multiple CR test case
- Clean up workaround code

The assertion was checking wrong variable (skip_back vs skip_bytes).
skip_back is search step size, skip_bytes is buffer offset needing validation.

Author: mohsinm-dev

Lib/test/test_io/test_textio.py

@@ -689,60 +689,21 @@ def test_multibyte_seek_and_tell(self):
     def test_tell_after_readline_with_cr(self):
         # Test for gh-141314: TextIOWrapper.tell() assertion failure
         # when dealing with standalone carriage returns
-        data = b'line1=1\r'
+        data = b'line1\r'
         with self.open(os_helper.TESTFN, "wb") as f:
             f.write(data)
 
         with self.open(os_helper.TESTFN, "r") as f:
             # Read line that ends with \r
             line = f.readline()
-            self.assertEqual(line, "line1=1\n")
+            self.assertEqual(line, "line1\n")
             # This should not cause an assertion failure
             pos = f.tell()
             # Verify we can seek back to this position
             f.seek(pos)
             remaining = f.read()
             self.assertEqual(remaining, "")
 
-    def test_tell_after_readline_with_multiple_cr(self):
-        # Test for gh-141314: TextIOWrapper.tell() assertion failure
-        # when dealing with multiple standalone carriage returns
-        test_cases = [
-            (b'line1\r\rline2\r', ['line1\n', '\n', 'line2\n']),
-            (b'line1\r\r\rline2\r', ['line1\n', '\n', '\n', 'line2\n']),
-            (b'line1\rline2\rline3\r', ['line1\n', 'line2\n', 'line3\n']),
-            (b'\r\rdata\r', ['\n', '\n', 'data\n']),
-        ]
-
-        for data, expected_lines in test_cases:
-            with self.subTest(data=data):
-                with self.open(os_helper.TESTFN, "wb") as f:
-                    f.write(data)
-
-                with self.open(os_helper.TESTFN, "r") as f:
-                    # Read all lines and call tell() after each
-                    lines_read = []
-                    positions = []
-                    while True:
-                        pos_before = f.tell()
-                        line = f.readline()
-                        if not line:
-                            break
-                        lines_read.append(line)
-                        # This should not cause an assertion failure
-                        pos_after = f.tell()
-                        positions.append((pos_before, pos_after))
-
-                    # Verify lines read correctly
-                    self.assertEqual(lines_read, expected_lines)
-
-                    # Verify we can seek back to each position
-                    f.seek(0)
-                    for i, (pos_before, pos_after) in enumerate(positions):
-                        f.seek(pos_before)
-                        line = f.readline()
-                        self.assertEqual(line, expected_lines[i])
-                        self.assertEqual(f.tell(), pos_after)
 
     def test_seek_with_encoder_state(self):
         f = self.open(os_helper.TESTFN, "w", encoding="euc_jis_2004")

Modules/_io/textio.c

@@ -2844,14 +2844,9 @@ _io_TextIOWrapper_tell_impl(textio *self)
     /* Fast search for an acceptable start point, close to our
        current pos */
     skip_bytes = (Py_ssize_t) (self->b2cratio * chars_to_skip);
-    /* Skip the optimization if next_input is empty */
-    if (PyBytes_GET_SIZE(next_input) == 0) {
-        skip_bytes = 0;
-    } else {
-        skip_back = 1;
-        assert(skip_back <= PyBytes_GET_SIZE(next_input));
-        input = PyBytes_AS_STRING(next_input);
-    }
+    skip_back = 1;
+    assert(skip_bytes <= PyBytes_GET_SIZE(next_input));
+    input = PyBytes_AS_STRING(next_input);
     while (skip_bytes > 0) {
         /* Decode up to temptative start point */
         if (_textiowrapper_decoder_setstate(self, &cookie) < 0)