fix code quality issues

[withshubh]

Description

Hi 👋 I work at DeepSource, I ran DeepSource analysis on the forked copy of this repo and found some interesting code quality issues in the codebase, opening this PR so you can assess if our platform is right and helpful for you.

Summary of changes

• Removed unnecessary use of comprehension …
• Used literal syntax instead of function calls to create data structure
• Used callable() to check if the object is calllable
• Refactored unnecessary else / elif when if block has a break statement
• Remove implicit object from the base class
• Added .deepsource.toml to continuously analyze the repo for code quality issues

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[withshubh]

@googlebot I signed it!

[cyrilchim]

Hi Shubhendra,

Thank you very much for the PR! DeepSource sound like a very cool project. Unfortunately, we can not integrate '.toml' to the library as we need to maintain sync between the internal and external versions of the repo.

If that is fine with you, I am happy to review the PR assuming we do not push '.toml' file.

[withshubh]

Hi @cyrilchim 👋

No worries! I removed the .deepsource.toml file.

I would really appreciate it if you could drop any suggestion on what we can do better to onboard you(or tf-quant-finance) on DeepSource. :)

[cyrilchim]

Sorry for the delay, Shubhendra.

This all looks good. I have only a minor comment on 'callable'.

Could you please also squash your commit?

Thank you!

[cyrilchim]

this is a legacy part to deal with Python 2.7. Since we now require Python >= 3.7, we can replace '_is_callable' with the in-built method 'callable'. Please do so or leave it as it is now