Fixes:
- PYL-W0612: Rename unused variable to `_`
- PYL-C0123: Use `isinstance()` for checking type
- PAP-W0011: Use `dict.items()` to iterate over a dictionary
- PAP-W0012: Use `dict.get()` to access value from dictionary instead of an `if` query to check whether the key exists
- PYL-C0325: Remove superfluous brackets `()`
- PYL-R1701: Merge multiple consecutive `isinstance()` calls into one