Why is there no main() function in Python?

In this article, we will understand why there is no main() function in Python.

There is no doubt that Python does not have a so-called main function, but, about "Main functions of Python" and " are often quoted on the Internet. It is recommended to write The main function. "

Their intention may be to replicate the original main approach, but many Be misled (or misunderstood) and create extremely complex code as a result.

Before we begin, we will answer the following two questions -

• What exactly is the "main function"?

• Why do some programming languages ​​need to use the main function?

Some programming languages, such as C/C, C#, Java, Go, Rust, etc., use The main function, as the execution entry of the program, has a specific meaning -

• This main function name is required, which means there must be a main function Function.

• Because there can only be one main function, each entry of the program is unique.

• The syntax format has specific requirements and follows a very consistent (fixed) template.

Why must we make the main entry function? compulsory?

These are compiled languages ​​that require the code to be compiled into an executable file operating system/bootloader binaries to find the program's startup, so you This function must be defined.

Simply put, there is an important beginning that must be defined in a large amount of content Executable code.

Main functions are the basic organic features of these languages.

But when we return to Python, things change dramatically.

• Python is an interpreted language, also known as a scripting language. this The running process runs from top to bottom, line by line, which means that its The starting point is known.

• Each .py file is an executable file that can be used as the entry point of a program, means that the entry point of the program is flexible and does not have to follow a convention Already following.

• When executing a Python project without specifying an entry file (the more A typical command line, such as "python -m http.server 8000"), may be due to There is a main.py file which does the following as a "file" in the package operate.

To sum up, the scripting language Python is different from the compiled language. it can Select flexible execution techniques at the level of individual modules (i.e. .py files), or at a package level consisting of many modules, unlike other languages ​​that cannot This can be achieved without clearly defined entries.

In other words, Python does not require programmers to specify a unified entry (either It is syntax level function, class or other).

Some users may be confused because they often encounter or write the following code -

# defining the main function using the def keyword
def main():
   ……
if __name__ == '__main__':
   main()

Isn’t this Python’s main function? I believe many people agree! -

No, it’s not.

Except the function name is "main", it has no connection with the orthodox main The function we described earlier, it is not required and does not necessarily control the order program execution. Without it, it won't cause any syntax problems.

Some people want to identify a "main" function to emphasize its "main" status and Make this the first function to be executed manually.

They may think that functions with such names are easier to remember.

They may want to write if name =='main' to prove that main() only runs under The current script is executed directly and should not be executed when imported. other modules.

However, we do not recommend this writing style.

The most common example: only a few dozen lines of code or a script file Implemented a simple function (a small crawler, using a turtle to draw a picture, etc.), But they are all written the same as before.

For the following reasons, it is not recommended to write if name__ == '__main' -

• First, if there is only one file because there is no export option.

• 2. If there are multiple files, write this sentence in the entry file (main.py) Strongly discouraged. Since it is the starting point, its content should not be exported for use in other modules.

• Finally, it is not possible to write this judgment in a non-entry file with many files. Recommended, since the most you can do is create some of these tests program. However, test code should be separated and stored in a separate Directory or file.

Every time I encounter this kind of complex code, I worry without thinking. Why Did you write the if statement? If possible, separate the main function, don't even Wrap it in a function!

Summarize

• Get rid of inertial thinking and build real code. Main entry function Is specific to some languages ​​and should not be used in Python. you should Understand the characteristics of scripting languages ​​and write them in a simple and understandable language Attractive style.

• Use main.py instead of main(). Because Python’s program execution unit is Script files instead of functions or classes, the entry file should be named main.py, Internal functionality is determined by requirements.

• If feasible, use main.py as the entry file. This file is very simple to put together and use Use the "-m" parameter on the command line.

in conclusion

In this article, we learned why Python, unlike other programming languages, lacks Main function. We also learned about the condition __name__ == '__main__'.

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