Which supervised learning algorithm to classify customers buying items
As per the problem statement statement it does look like 3 class classification problem. 
But I don't think you can use any ML algorithms using Python without sklearn package in it. Try getting it installed and you can implement the problem using Logistic regression, Decision Tree, there are still more classification algorithms.
However if you are planning to extract a pattern from the dataset and making into cluster, you can use K-means clustering which is a un-supervised algorithm.