Fix some bug risks and code quality issues

[sanketsaurav]

Hi! 👋

I'm the founder of DeepSource, a code review automation tool that detects problems in every PR using static analysis and helps developers save a ton of time during code reviews. I ran our analysis on this project and found some interesting issues. I've already fixed some of them in this PR. Here are some others that you might find interesting:

• Duplicate dictionary keys
• Statement doesn't have any effect
• Consider iterating dictionary

Here are some of the fixes I've made in the PR:

• (anti-pattern) Replace unnecessary function calls to dict() and list() with literals
• (bug-risk) Replace calls to exit() with sys.exit()
• (anti-pattern) Remove unnecessary lambda expression

I would love it if you use DeepSource for running continuous analysis on the project. It's free for open-source and detects 550+ issues in Python. All you need to do is follow these simple steps:

1. Merge this PR
2. Sign up on DeepSource with your GitHub account and grant access to this repo.
3. Activate analysis on this repo here.
4. Done! 🎊

Finally, please LMK if you have any questions that I can answer. Looking forward to seeing DeepSource running on aardvark! 🙌

Best, Sanket.