Fix a few performance and code quality issues

[de-sh]

Hi, I had recently run through your project and decided to check it with a static analyzer and found some interesting and concerning issues related to performance, bugs and security flaws. You can find the report here. I have used DeepSource's auto-fixer to fix a few, I hope to work on the rest soon.

Changes:

• Remove unnecessary list comprehension
• Remove unnecessary call to dict()
• Remove unnecessary if statement in assignment
• Add .deepsource.toml file to file to run continuous static analysis on the repository with DeepSource

I strongly recommend that you do enable DeepSource analysis after merging this PR, as it is free for OpenSource projects. If you are interested, please follow these steps:

• Sign up on DeepSource with your GitHub account and grant access to this repo.
• Activate analysis on this repo.
• You can also look at the docs for more details. Do let me know if I can be of any help!

[de-sh]

BTW, going back in time, I see that DeepSource was earlier enabled on this repo. May I know if there were any issues you faced because of which you decided to remove the same.