I would like to know if there is a way to incorporate an external csv file into a custom made python script in ArcMap field calculator. I am inputting fields from the current layer, but need to access an external csv containing the mapping for these fields to convert them to values of interest. Is this at all possible?
Yes, as @Fezter commented:
if you wanted to you could import the csv module and read the file that way
but I think it would be easier to just use the Join Field tool:
Joins the contents of a table to another table based on a common attribute field. The input table is updated to contain the fields from the join table. You can select which fields from the join table will be added to the input table.
The records in the Input Table are matched to the records in the Join Table based on the values of Input Join Field and the Output Join Field. Optionally, only desired fields can be selected from the Join Table and appended to the Input Table during the join.