looping over variables in data field extraction – python

I am currently using spark on python to extract data from a SQL database. However each field has 4 instances of data, e.g. cat_i1, cat_i2, cat_i3, cat_i4, var_i1, var_i3, var_i4 etc…

The code I am using looks as follows:

field_names = ["cat_i1, var_i1"] ,

df = retrieve_fields(names=field_names, engine=dxdata.connect())

for the instance 1 dataframe

I am looking for a way to get each instance in the dataframe without typing it manually. I am new to python so unsure how I would use loops (or any other method), to do this.
Can anyone help?
Thank you.

>Solution :

You can just specify the general fields and then create the instances iterating through them:

fields = ["cat", "var"]
inst = [f + "_i{}".format(x) for x in range(1,5) for f in fields]