Unique Key - CustomerID, A Categorical or a Numerical Variable?
I don't think you should use customerID as a variable. This is an unique value for each customer. It can be used as an index - to know for what customer belongs the prediction.
So you'de better drop this column from training/test data.
I am trying to do Segmentation in Customer Data in Python using Pandas. I have a customer ID variable in my dataset. I am confused over here, even though it won't be considered as a variable that affects the Output variable. How do we actually treat this variable if needed, a Categorical or a numerical ? 
Also, Is there a business case that you could think of where the customerID will be considered?