Your search query "linkto%3A%22Asking for Help%2FDo you need a int main() like you do in c%2B%2B%22" didn't return any results. Please change some terms and refer to HelpOnSearching for more information.
(!) Consider performing a full-text search with your search terms.

Clear message

Do you need a int main() like you do in c++ here?

I am a Newbie to python and need to know if there is a int main that is the body of the program.

There's no requirement to have a main function in Python, but there is the concept of a main module. But let us first consider what happens when you run a Python file.

Consider a Python file called program.py. If we run this file, the content of the file is executed. So you may have some functions and classes and perhaps some normal statements as follows:

class C:
    def method(self, arg):
        ...

def func(x, y, z):
    ...

answer = func(1, 2, 3)
print "Answer is", answer

Here, the class C gets created, as does method inside the class, and the function func gets created. At this point, no code inside method or func is run, but these things are now defined in the module. Then, the statements at the end are run, and the first one does call func. Finally, a print statement is executed.

Now, if this file were to import other modules, the content of those modules would be executed in the same way. So if we add the following to program.py...

import mymodule

...then that module, perhaps defined in mymodule.py, would be loaded and run in the same way. Let's say that the module is written as follows:

def modfunc(a, b):
    ...

print test_the_function(123, 456)

Even if you import mymodule, with the code as it is, the modfunc function will be defined, but then the print statement will be run and you'll get something printed out, even though that probably isn't what you want.

So what people do in Python is this:

def modfunc(a, b):
    ...

if __name__ == "__main__":
    print test_the_function(123, 456)

When mymodule is imported, the code is run as before, but when we get to the if statement, Python looks to see what name the module has. Since the module is imported, we know it by the name used when importing it, so __name__ is mymodule. Thus, the print statement is never reached.

However, we might want to be able to run mymodule.py directly. If we do that, the code is run as before, but at the if statement when Python looks for the module name, since the code was not imported but actually run directly, the value of __name__ will be __main__. Thus, the print statement will be reached and you'll be able to test the code.

So in summary, by testing the __name__ in a Python file, you can find out whether the file is the one being run directly because it will have the value __main__. Otherwise, it will have another value. Some people tend to write code like the following to emulate a main function:

def main():
    ...

if __name__ == "__main__":
    main()

But there's really no requirement to have such a function: it's just a convention.


CategoryAskingForHelp CategoryAskingForHelpAnswered

Unable to edit the page? See the FrontPage for instructions.