a -very- case sensitive search

[Ola K]

Hi,
I am pretty new to Python and I want to make a script that will search
for the following options:
1) words made of uppercase characters -only- (like "YES")
2) words made of lowercase character -only- (like "yes")
3) and words with only the first letter capitalized (like "Yes")
* and I need to do all these considering the fact that not all letters
are indeed English letters.

I went through different documention section but couldn't find a right
condition, function or method for it.
Suggestions will be very much appriciated...
--Ola