add a python script to an input file

There is no thing like adding a (Python) script to an input file. But for your purpose, what you may need is to read the input file via Python script and perform the required changes to the same input file.

Please let us know what exactly you need to do if the above doesn't answer your query.

Regards

You may read the input file as a regular text file and add/insert commands wherever necessary. OR

You may use the scripting functionality keywordBlock at the end of your python script to add stuff to the input file just created by the script.