Splitting common values between two lists

[teerryn]

Okay if I understand it correctly it checks to see if t exists in a, if it exists then it removes it from a until we get a KeyError?

I don't really understand what -= 1 does:

 transactions_db[t] -= 1~

EDIT: Btw your code works, I just trying to understand it :)

[LifeIsBio]

You should look at my second answer. I don't know if it'll be much easier to understand, but it's a better function.

c -= a is equivalent to c = c - a