What minimum should a person know before saying "I know Python"

[Aseem Bansal]

I understand that being able to solve problems and knowing when to use something is the final measure of knowing something properly. 

But I wanted to find something quantitative that I can use to measure myself. Like the interview questions that Tim Chase posted.

Measuring myself based on the problems that I can think of is like a small child saying "I know that 1 + 1 = 2. So I know maths". That may be the toughest problem that he can think of. That isn't a correct evaluation of his math abilities. Similarly measuring myself on the basis of the problems that I can think of and solve doesn't actually measure anything.

I don't want to be living in a fool's paradise based on solving the problems I can solve. It is not being able to solve a problem that will make me realize my limits.

That's why I asked this question... I am kind of asking for advice.