I know that lambda is anonymous function, and there's no need to create variable for lambda, but here we need to meet the interface requirements. Requirement here is that check is callable.

In real world I would not create function for this one liner, that's why I'm showing solution with lambda.

You need more corner-case tests here

I'm not happy with this kata. Using builtin function is not cheating when in description is no information about not using this.
Also this "anti-cheat" was not giving me option to name my variable max :/

Hi, after attempts I have this error. Should it be visible or I just made something wrong?

Traceback (most recent call last):
File "main.py", line 60, in
rand = sample([x for x in c.dict.keys() if not str(x).startswith('__')], 1)[0]
File "/usr/local/lib/python2.7/random.py", line 325, in sample
raise ValueError("sample larger than population")
ValueError: sample larger than population