ex1.py. Python works best with files ending in .py.https://learnpythonthehardway.org/book/ex1.html Exercise 1: A Good First Program Warning If you skipped Exercise 0 then you are not doing this book right. You must read every single thing I write here and read it carefully. For example, are you trying to use Python 3 for this book? I said in Exercise 0 to not use Python 3, so you should not use Python 3. Are you trying to use IDLE or an IDE? I said not to use one in Exercise 0, so you should not use one. If you skipped Exercise 0 please go back to it and read it. You should have spent a good amount of time in Exercise 0 learning how to install a text editor, run the text editor, run the Terminal, and work with both of them. If you haven't done that, then do not go on. You will not have a good time. This is the only time I'll start an exercise with a warning that you should not skip or get ahead of yourself. Type the following text into a single file named...