Flask (Werkzeug) Templating Caused Trackback Loop Reference Issue
Today, I was facing an issue when using
If use an dash “-“ linked variable name in Flask template, it will cause Flask to hang without
throwing any exception.
At beginning, I guess it may be an issue of
Jinja template rending. But after traced in IDE
(Pycharm community 2019.3), I saw that templating raised the exception and
Werkzeug is handling.
At first I uses Flask debug mode and IDE debug run to step into codes to dig it. IDE gets
slower and slower and the debugger hung in
Eventually, I found an endless loop in
Python\Lib\traceback.py to walk trackback stacks. The
trackbacks are stored in a link which nodes point to next. In
werkzeug\debug\tbtools.py, the exception was catched. In
Werkzeug wants to log it and print it out.
The trackback link has looped reference as below picture.
Simple code to re-produce it as below (“font-size” variable caused.).
Raised Github issue at
- Window 10
- Python 3.6.8150.1013 (venv)
- Flask 1.1.1
- Werkzeug 0.16.1
Possible related Python issue:
- Issue9427 - logging.error(‘…’, exc_info=True) should display upper frames, too
- Issue1553375 - Add traceback.print_full_exception()
– END –