In it’s most simplistic way, we can declare an inargument or inoutargument which the excel activity can populate. Same inargument or inoutargument then can be used as input to the python script. Assumption here is that the python script knows how to handle the input and it is designed accordingly.
Further, are you trying to run a python script in every excel loop iteration ? I do not know your use case … will it not be better if we can run the script once the excel loop is complete … i.e. write the excel loop final output to an argument then pass the same to python script ?