Double Unders

I think the problem is that when this video for double unders and if __name__ == '__main__' comes up, they haven't really gotten to the concept of importing files yet.

So, you can have different pieces of code in completely different files, and import one file into another. That way you can re-use functions and so on over and over. You could write something like this:

# Here's a function.
def say_hi():
    # Do some stuff here...
    return "Hi!"

# Here are some commands.
greeting = say_hi()
print("I'm in the hi.py file, and I'm saying: ", greeting)

...and save it in a file called hi.py. (You can even do this in Workspaces.) Then, if you want to use that function in a totally different program, you can write a script in another file, like this:

import hi

aloha = hi.say_hi()
print("Hawaiians say aloha when they mean ", aloha)

...and save it as aloha.py. Now you can use the function from one file in a program in another file. But, now if you run aloha.py, the first thing it does is import the file hi.py, and every bit of code in it will immediately and automatically run. And you'll get this (even if you don't want it):

>>python aloha.py

I'm in the hi.py file, and I'm saying: Hi!
Hawaiians say aloha when they mean Hi!
>>

The only way to stop that from happening is to check to see what the file's __name__ equals. The file that you command to run is always named __main__, and any file that's imported is given its own filename as a name. So when aloha.py imports the file hi.py, the code inside that file is set to '__hi__', not '__main__'. Since it's been imported and not told to run itself, if __name__ == '__main__' will be False, and if you put the code you don't want to always run inside an if __name__ == '__main__' block, the code won't run unless/until some line in aloha.py specifically tells it to.