I understand you divide $Q$, which is the set of all terminal histories into subsets $Q_1,..., Q_n$.
What is the probability of reaching some subset $Q_i$? Is it just the product of chance probability, the opponent's probability, and my probability?
As I understand it, the sampling only occurs in the opponent's information sets. How does that work? If there are two players, player 1 strategy is based on what strategy I use.
What happens after you have determined a subset $Q_i$ you want to sample? How many times do you iterate over the subset $Q_i$?
I have searched around and I cannot find any Python code that uses external sampling, but plenty of papers that give formulas, but do not explain the algorithm in detail. So, a Python example of MC-CFR external sampling would probably make it a lot easier for me to understand the algorithm.