If you know what skills you are looking for (hint: lots of companies and recruiters don't), this is not actually that hard.
For every skill, there are questions that should be really easy to answer for everybody with expertise, but are suprising/hard to answer for everybody who pretends to have knowledge. This enables you to check quite quickly whether the claimed skills are actually there or not.
For example, the easier sections in
> https://github.com/satwikkansal/wtfpython
might give you a hint for topics that most seasoned Python programmers should know blindfolded while they are probably rather surprising for anybody with shallow Python knowledge. Let the applicant explain how they came up with their solution for, say, some of the problems, and you will see rather fast whether the claimed skills are actually there or not.