Refactor code

[LyndonFan]

Addresses most issues in #95

• Fixed 2 instances of unnecessary else
• Fixed 2 instances of using range(len(...))
• Fixed 1 instance of code complexity by removing unnecessary "is not None" check
• Fixed 1 instance of code security by using requests.get instead of urllib.request.urlretrieve

There is still 1 instance of code complexity issue remaining. I have performed some minor refactoring, but it's still too complex according to codefactor.io.

[LyndonFan]

The new code has passed all the checks. Would it be possible to get a review?

[Alexsandruss]

I see no problems, let's wait for at least one additional approve.