The documentation of how to use snakemake contains the following statement:

The parameters set with the params keyword, can be accessed in your python script via snakemake.params[i] or snakemake.params.name_of_param. Accordingly one can use snakemake.input or snakemake.output.

This is great to use in python, but intrinsically these parameters are of a snakemake specify type and need casting before usage. Perhaps that should be added to the documentation.