对目录中的每个文件执行相同的命令

I am hoping for basic help in constructing a python script for taking each file in a directory and executing the same task on each one. I have a large number of protein files (FASTA format), and the program I'm using only allows for ~500 entries to be searched at once. So, I need to run the program for each of my 116 files separately, with various options, like "-N" and "-t 0.800". I searched for help, and I know I have to import os etc., but I've never worked with these sorts of system commands and am lost. Any help is appreciated!I am hoping for basic help in constructing a py