Define categorical variable in PoissonGAM

[Ccccr4]

First of all, thanks for providing a such useful package. I have some questions regarding to the usage.

1. I tried to use f() to model the categorical variable in the data. However, I could not find a way to define a reference level for the category variable
2. Based on the description of FactorTerm (f()), it seems that when there are k categories in this variable, k coefficients will be given by the model. I thought when it is a k-category variable, only k-1 coefficients should be given?
3. When I used PoissonGAM.coef_ to extract the coefficients of the paramters, it only gives an array. Is there a way to show the variables and coefficients side by side? Thanks for your help in advance!