if __name__== "__main__"do?
I've seen some code samples and tutorials that use
def main(): # my code here if __name__ == "__main__": main()
But why? Is there any reason not do define your functions at the top of the file, then just write code under it? ie
def my_function() # my code here def my_function_two() # my code here # some code # call function # print(something)
I just wonder if there is any rhyme to the main?
Without the main sentinel, the code would be executed even if the script were imported as a module.
Everyone else has already answered it, but I think I still have something else to add.
Reasons to have that
if statement calling
main() (in no particular order):
Other languages (like C and Java) have a
main() function that is called when the program is executed. Using this
if, we can make Python behave like them, which feels more familiar for many people.
Code will be cleaner, easier to read, and better organized. (yeah, I know this is subjective)
It will be possible to
import that python code as a module without nasty side-effects.
This means it will be possible to run tests against that code.
This means we can import that code into an interactive python shell and test/debug/run it.
def main are local, while those outside it are global. This may introduce a few bugs and unexpected behaviors.
But, you are not required to write a
main() function and call it inside an
I myself usually start writing small throwaway scripts without any kind of function. If the script grows big enough, or if I feel putting all that code inside a function will benefit me, then I refactor the code and do it. This also happens when I write
Even if you put code inside the main function, you are not required to write it exactly as that. A neat variation could be:
import sys def main(argv): # My code here pass if __name__ == "__main__": main(sys.argv)
This means you can call
main() from other scripts (or interactive shell) passing custom parameters. This might be useful in unit tests, or when batch-processing. But remember that the code above will require parsing of argv, thus maybe it would be better to use a different call that pass parameters already parsed.
In an object-oriented application I've written, the code looked like this:
class MyApplication(something): # My code here if __name__ == "__main__": app = MyApplication() app.run()
So, feel free to write the code that better suits you. :)