Check says FAIL, when it shouldn't (tested)

I would like to give some feedback about ...

From: http://www.checkio.org/mission/most-wanted-letter/solve/

Hello,

I have spent a few hours doing this exercise, given that I am a beginner in Python. After finally fixing my code so that it gives out correct solutions, the Checkio interface doesn't allow me to pass the 3rd test. In fact, every time I run the code, it says that the most valuable letter is "o", no matter what the case is.

I have tested the code with the Python Shell, codeskulptor.org and pythontutor.com and got the correct solutions on all of them, with various examples.

I repeat, I am a beginner and my code probably isn't top-notch, but it seems to be working just find elsewhere.

I have put in hours of work into this, so I would hate for my efforts to go to waste.

Sincerely, Nahlim

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