bpo-30597: Shows expected input in custom 'print' error message

Lib/test/test_print.py

@@ -128,5 +128,26 @@ def flush(self):
  raise RuntimeError
  self.assertRaises(RuntimeError, print, 1, file=noflush(), flush=True)
 
+
+class TestPy2MigrationHint(unittest.TestCase):
+ """Test that correct hint is produced analogous to Python3 syntax,
+ if print statement is executed as in Python 2.
+ """
+
+ def test_normal_string(self):
+ python2_print_str = 'print "Hello World"'
+ with self.assertRaises(SyntaxError) as context:
+ exec(python2_print_str)
+
+ self.assertTrue('print("Hello World")' in str(context.exception))
+
+ def test_string_with_soft_space(self):
+ python2_print_str = 'print "Hello World",'
+ with self.assertRaises(SyntaxError) as context:
+ exec(python2_print_str)
+
+ self.assertTrue('print("Hello World", end=" ")' in str(context.exception))
+
+
 if __name__ == "__main__":
  unittest.main()

Objects/exceptions.c

@@ -2862,6 +2862,51 @@ _PyErr_TrySetFromCause(const char *format, ...)
  * or minus, using the stream redirection syntax).
  */
 
+
+// Static helper for setting legacy print error message
+static int
+_set_legacy_print_statement_msg(PySyntaxErrorObject *self, Py_ssize_t start)
+{
+
+ PyObject *strip_sep_obj = PyUnicode_FromString("\r\n");
+ Py_UCS4 soft_space_check = PyUnicode_READ_CHAR(PyUnicode_FromString(","), 0);
+
+ if (strip_sep_obj == NULL)
+ return -1;
+
+ // PRINT_OFFSET is to remove `print ` word from the data.
+ const int PRINT_OFFSET = 6;
+ Py_ssize_t text_len = PyUnicode_GET_LENGTH(self->text);
+ PyObject *data = PyUnicode_Substring(self->text, PRINT_OFFSET, text_len);
+
+ if (data == NULL)
+ return -1;
+
+ data = _PyUnicode_XStrip(data, 1, strip_sep_obj);
+
+ Py_DECREF(strip_sep_obj);
+
+ // gets the modified text_len after stripping `print `
+ text_len = PyUnicode_GET_LENGTH(data);
+ const char *maybe_end_arg = "";
+
+ if (text_len > 0) {
+ if (PyUnicode_READ_CHAR(data, text_len-1) == soft_space_check) {
+ maybe_end_arg = " end=\" \"";
+ }
+ }
+
+ PyObject *error_msg = PyUnicode_FromFormat(
+ "Missing parentheses in call to 'print'. Did you mean print(%U%s)?",
+ data, maybe_end_arg);
+
+ Py_DECREF(data);
+
+ Py_XSETREF(self->msg, error_msg);
+
+ return 1;
+}
+
 static int
 _check_for_legacy_statements(PySyntaxErrorObject *self, Py_ssize_t start)
 {
@@ -2897,9 +2942,8 @@ _check_for_legacy_statements(PySyntaxErrorObject *self, Py_ssize_t start)
  }
  if (PyUnicode_Tailmatch(self->text, print_prefix,
  start, text_len, -1)) {
- Py_XSETREF(self->msg,
- PyUnicode_FromString("Missing parentheses in call to 'print'"));
- return 1;
+
+ return _set_legacy_print_statement_msg(self, start);
  }
 
  /* Check for legacy exec statements */