Why doesnt Python have a main function? Why dont I recommend writing the main function?

without doubt Python There is no such thing as main Entry function , But I often see some articles on the Internet “Python Of main function ”、“ Suggest to write main function ”……

Some people know it , His intention may be to imitate those authentic main function , But a lot of people are obviously misled （ Or I misunderstood ）, It's very cumbersome code to write .

In this issue “Python Why? ” Let's talk about it Python Why not? main function ？

Before we get to the point , Let's first answer these two questions ： So-called “main function ” What is it? ？ Why do some programming languages have to force a main function ？

Some programming languages use main Function as the execution entry of the program , for example C/C++、C#、 Java、Go and Rust etc. , They have a specific meaning ：

• main Function names are mandatory , That is to say, there must be a main function
• main There can only be one function at most , In other words, the entry to the program is unique
• There are certain requirements for grammatical format , With a relatively fixed template

Why force a main The entry function ？

These are compiled languages , You need to compile the code into executable binaries , To make the operating system / The starter finds the starting point of the program , So we have to agree on this function . In short , It's in a lot of code , You need to define a significant start for execution .

It's not hard to see. ,main Functions are an important and indispensable part of those languages .

However , Let's see Python, The situation is very different .

• Python It's interpreted language , Script language , The running process is from top to bottom , Run line by line , That is to say, its starting point is knowable
• Every .py A file is an executable file , Can be used as the entry file of the whole program , In other words, the entry of the program is flexible , There is no agreement that must be observed
• Sometimes run Python project , There is no entry file specified （ More common on the command line , for example "python -m http.server 8000"）, It could be there __main__.py file , The bag it's in is treated like a “ file ” Here we go

It comes down to , mean Python This scripting language is different from compiled languages , It doesn't matter at the single module level （ That is, a .py file ）, Or at the package level of multiple modules , You can choose flexible execution methods , Unlike other languages, they can't execute without the agreed entry .

in other words ,Python There is no need to specify at the syntax level that programmers must define a unified entry （ Whether it's a function or a class or something ）.

Some students may have doubts , Because they often see or write the following code themselves ：

# main There's some body code in it
def main():
……
if __name__ == '__main__':
main()

Isn't that Python Of main Function ？ I believe many students will think so ！

no ！ no ！

Except that the function name is “main” outside , It's the same as the orthodox main Functions have nothing to do with half a cent , There is no compulsion , Nor does it necessarily determine the sequence of program execution . It's missing , It won't lead to any grammar problems .

The reason why some insiders want to name one ”main“ function , Actually, I want to emphasize it ” The main “ status , Want to artificially arrange it as the first function to execute . They might think of a function named like this , It's easier to remember .

The reason why some insiders want to write if name == '__main__' , May want to show main() Run only if the current script is executed directly , Do not want to be imported into other modules to run .

For these “ insider ”, They have a point .

however , I personally don't recommend it , And sometimes it's very disgusting ！

The most obvious example ： There are only dozens of lines of code , Or just one script file , Implement a simple function （ A little bit of a reptile 、 use turtle Draw a picture and so on ）, But they're all written in the previous style .

Every time I see this kind of unthinkable and cumbersome code , I feel sick . Why write that line if Sentence? ？ If possible , It should be split main function , It doesn't even have to be encapsulated as a function ！

I personally sum up the following experience ：

• Break the habit of thinking , Write authentic code .main Entry functions are specific to some languages , It's not supposed to be here Python in “ Copy sth. without catching its spirit ”, You should understand the characteristics of scripting languages , Write a simple and elegant style
• Use main.py Instead of main(). because Python The execution unit of a program is actually a script file , Not a function or class , So it is suggested to name the entry file as main.py, Internal functions depend on demand
• If you can , Use __main__.py As an entry file . This file combines the “-m” Parameters use , Very easy to use .
• It is not recommended to write if name == '__main__'. First , If there's only one file , Because there is no possibility of export , Not recommended . secondly , When there are multiple files , Entrance file （main.py） It is not recommended to write this sentence , The code logic of this file should be refined , In theory, its content should not be exported to other modules for use , Because it's the starting point ！ Last , It is not recommended to write multi file non entry files , Because this judgment is written in the non entry file , The biggest function is to write some test code , But the test code should be separated , Write to a special directory or file .

Summary ： This paper first explains what is main Entry function , And why some languages are forced to write main function ; next , Explained why Python No need to write main function ; Finally, it is aimed at some people's habitual misunderstanding , I share four personal programming experiences .

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