Fix Deepsource issues (#2085)

* DeepSource issue: Built-in function `len` used as condition

Using the `len` function to check if a sequence is empty is not idiomatic
and can be less performant than checking the truthiness of the object.

`len` doesn't know the context in which it is called, so if computing the
length means traversing the entire sequence, it must; it doesn't know
that the result is just being compared to 0. Computing the boolean value
can stop after it sees the first element, regardless of how long the
sequence actually is.

* DeepSource issue: Consider using literal syntax to create the data structure

Using the literal syntax can give minor performance bumps compared to
using function calls to create `dict`, `list` and `tuple`.

This is because here, the name dict must be looked up in the global
scope in case it has been rebound. Same goes for the other two types
`list()` and `tuple()`.

* DeepSource issue: Consider decorating method with `@staticmethod`

The method doesn't use its bound instance. Decorate this method with
`@staticmethod` decorator, so that Python does not have to instantiate
a bound method for every instance of this class thereby saving memory
and computation. Read more about staticmethods here.

* DeepSource issue: Consider using `in`

To check if a variable is equal to one of many values, combine the values
into a tuple and check if the variable is contained `in` it instead of
checking for equality against each of the values. This is faster, less
verbose, and more readable.

* DeepSource issue: Implicit enumerate calls found

Using `range(len(...))` is not pythonic. Python does not have not
index-based loops. Instead, it uses collection iterators.

Python has a built-in method enumerate which adds a counter to an
iterable. Using this, you can access the counter and the value from
the iterable at the same time. It is therefore recommended to replace
`range(len(...))` with `enumerate(...)`.