I do have experience using probably 20-30 different bug trackers, installed or hosted and so far if you are up to deal with a big number of bugs and you want to spend less time coding-the-issues-tracker, to get Atlassian Jira, which is free for open-source projects.
Yes, it's not Python, it is Java, starts slowly and requires lots of resources. At the same time, RAM is far less expensive than your own time and if you want to extend the system you can do it in Python by using https://pypi.python.org/pypi/jira-python/
Do you think that Jira is the most used bug tracker for no reason? It wasn't the first on the market, in fact is quite new compared with others.
Once deployed you can focus on improving the workflows instead of patching the bug tracker.
One of the best features that it has is the ability to link to external issues and be able to see their status, without having to click on them. As an warning, for someone coming from another tracekr you may discover that there are some design limitations, like the fact that a bug can have a single assignee. Don't be scared about it, if you look further you will find that there are way to assign tickets to groups of peoples.