Your code fails for 143 = 13 * 11, or other numbers which have prime factors other than 2,3,5 and 7

Good for simplicity, bad for your algorithm knowledge.

Bloody hell, I did not realize the property of sets. That's very clever.

Solved

Yes, but here also some solutions should be filtered out.
Or there should be better guidelines how to write tests, to not let cheat them in many different ways.

Don't you just love how Python does most of the work for you? ^_^

@stealthguy Don't worry I felt the same way particularly when I hit convert("hello", allow, hex) # 320048

It appears that the alphabets are indexed from 0, so z would be 25, a, 26, and b would be 27 if iterating past the last element restarts at the first element.

@stealthguy I don't even see katas you authored when visiting your profile. Have you deleted them?

in link you gave a === 1, in this kata a === 0

Sometimes readability is more then fast execution. But yes I totally agree to you. I signed up here because I wanted to see not just how others solve some problem but also what solution is considered "best" by majority. Then I expected there to be microforum for every kata where discussion about why this and that is better. Simple "best practice" tag without comments are often not there yet. There is lot of work to be done...

You are wrong, it does not imply there will be only two parameters. It will work with arbitrary amount of parameters and is actually more universal, because it will also handle named parameters as well.