[Python-ideas] Just main (original) (raw)

anatoly techtonik techtonik at gmail.com
Tue Jun 19 09:52:36 CEST 2012

On Mon, Jun 18, 2012 at 9:59 PM, Jeremiah Dodds <jeremiah.dodds at gmail.com> wrote:

Andrew McNabb <amcnabb at mcnabbs.org> writes:

I'm not sure if a "main" function would add enough value, but I think it would add more value than a "main" boolean. +1 .

My first thoughts is that main() as a function is bad for Python, and here is why.

In C, Java and other compiled languages so-called main() function is the primary execution entrypoint. With no main() there was no way to instruct compiler what should be run first, so logically it will just start with the first function at the top (and if you remember early compliers - you can only call functions that are already defined, that means written above yours). Code exection always started with main(). It was the first application byte to start with when program was loaded to memory by OS.

In Python execution of a program code starts before the if name == 'main' is encountered (and it's awesome feature of a scripting language to start execution immediately). With automagical main() function it will also start before. That's why main() will never be the substitution for the classical C style entrypoint.

In Python entrypoint is a module (entrypoint namespace). name is equal to 'main' not only in a script, but also in console. And main as a flag in this namespace correctly reflects this semantic

So, main() function is not equivalent to C/Java entrypoint. However, a function like this may play an important role to mark the end of the "import phase" or "initialization phase". A high level concept that is extremely useful for web applications/servers/frameworks, who need to know when an application processes can be more effectively forked.

Here is one more problem - when module is executed as a script, it loses its name, which becomes equal to 'main'. I don't know if it ever caused any problems with imports or consistency in object space, or with static imports - it will be interesting to know any outcomes. What if module name always meant module name? But that's another thread. As for main - in this case instead of boolean it could be the name of the entrypoint module, and the check would be if name == main without quotes.

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