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In Python why a function called main doesn't have any special significance like it has in C and Java?

What if a programmer switches from C or Java to Python. Should he keep using main in Python also like in C or Java as it's his style now to do the programming or in a broad sense it is somehow harmful for doing programming in Python?

Edit: I have gone through this article where it was mentioned by a very good example why first time programmers should refrain main in python main in python harmful.

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  • Here's a counter-question to you: Why should it be meaningful in any language? Contemplating that will answer this. Commented Aug 13, 2012 at 6:37
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    Because that's "just how Python works" .. however, consider that, unlike C or Java the entire Python file (class, def, import, etc.) is just executed code! There is no separation of "definitions" and "executable code". Thus the file itself is the entry-point of execution! Commented Aug 13, 2012 at 6:37

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You should also be asking, why in C and Java does main have a special significance. It's just a choice on the part of the language designer. main could well have been called start or begin but somebody chose main and it stuck.

In Python there is no reason why you can't call a function main and have it be the start point of your program. However, Python has its own syntax to identify whether a certain file is the equivalent of main:

__name__ == "__main__"

This is typically wrapped as part of an if and could simply have a single line within calling your main function that actually starts your program.

Part of the design of Python and many (all?) scripting languages is that code can simply be written inline. You don't have to wrap everything in a function. As such, many simple scripts do not require any functions at all. A cron job for example that rotates log files could just be written as a block of code in a python file with no functions being defined.

In that scenario, the main method just isn't required.

Not requiring a main in many ways makes the language more flexible, especially for simpler tasks.

ADDENDUM:

To add some context to your edit. That article presents a very poor argument. In reality function name collisions are not uncommon as there are many modules that do the same or similar things (not so much in core but as soon as you start using pip you'll encounter the odd collision). Therefore it is beneficial to use descriptive function names and avoid ever doing a from foo import *.

In the same way that C++ programmers generally consider it bad form to pollute your namespace with using namespace std, Python programmers typically consider it bad form to pollute your namespace with import *, especially as it can cause a snowball effect if used everywhere.

Finally, you're unlikely to call 2 functions in your program main. You're much more likely to have name collisions elsewhere. The real danger is the wildcard import, not the main function.

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Such a programmer should do this:

if __name__ == "__main__": # run stuff

The variable __name__ is set to "__main__" if the module is not imported.

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No, the module or file can be imported, but the code inside the if condition will not run, like @Blender pointed out in his answer.
Right, I misread it. Thought you meant the module is not imported if if __name__=='__main__' is used. My bad, sorry
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In Python, there is something that acts like that main() function:

if __name__ == '__main__': # Your main function

The code in this if block is only run if the Python file has not been imported as a module.

If you're determined to use that ugly main() function, the Python equivalent would be something like this:

def main(): # ... if __name__ == '__main__': main()

I don't find it very pretty.

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In python a .py file can be used as either a module or can be run directly , so main is used to identify which part is to be run if the file is run directly or if the file is imported as module.

file.py:

def func(x,y): print x+y if __name__=='__main__': func(5,2):

if executed directly it prints 7

when imported , the main part doesn't runs:

>>> from so32 import * >>> func(5,5) 10 >>> func(10,20) 30
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In Python why a function called main doesn't have any special significance like it has in C and Java?

Because python wasn't design with C, java or such languages in mind, there are some languages that actually don't use main, http://c2.com/cgi/wiki?HelloWorldInManyProgrammingLanguages has quite a large number of hello world programs as you can see not all use main, though you probably can't really compare them all ...

Either way as others have stated you can check if a module has being directly ran from the interpreter by checking if __name__ == '__main__': oh and here are some tips from Guido Van Russon the creator of python on how to write main functions.

What if a programmer switches from C or Java to Python. Should he keep using main in Python also like in C or Java as it's his style now to do the programming or in a broad sense it is somehow harmful for doing programming in Python?

when you write python code, or for that matter when you write any program always try to have code seem natural in that language, this means following standards and practices either set by the language developers or the community at large, please don't write c or java like code in python its possible but its frown upon, the code tends to be error prone, and very difficult to understand, and sometimes quite slow, the same applies to any other language.

this has quite few good references Python coding standards/best practices

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There is an excellent explanation of why using main() to call individual procedures(or methods) is a good idea, by Kent D Lee in YouTube - basically it's because without main() all your variables are global and not only do they take longer to access, they also run the risk that one procedure's variables will interfere with those of another procedure. Also using main() to call your procedures enables you to reuse those procedures in another program by importing them. Additionally you can test individual procedures without executing the whole program. Of course if all you are going to do is output "hello world" it is no advantage at all to have a main method, and the only reason you would do it is to find out how it works.
The reason why everyone says that Python is good for learners is because you can start doing things straightaway very easily - the trouble is that if you are going to write sizeable programs you are soon faced with the fact that all those complications that other languages have, are actually quite important.

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