In importlib a verbose message can be formatted twice, the first time before passing it to _verbose_message(), and the second time in _verbose_message(), Example: $ python -v ... >>> open('{0}.pyc', 'wb').close() >>> __import__('{0}') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "<frozen importlib._bootstrap>", line 969, in _find_and_load File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked File "<frozen importlib._bootstrap>", line 673, in _load_unlocked File "<frozen importlib._bootstrap_external>", line 658, in exec_module File "<frozen importlib._bootstrap_external>", line 869, in get_code File "<frozen importlib._bootstrap_external>", line 440, in _validate_bytecode_header File "<frozen importlib._bootstrap_external>", line 368, in _verbose_message IndexError: tuple index out of range Proposed patch fixes the issue.