DetectNoMainFunction Decision Problem

Benedek Kaibas, Abishek Dhakal, Will Bennett

September 8, 2025

What is the main function in Python?

The main function in Python is declared, like this: def main(some parameter):

The if __name__ == "__main__" guard checks whether a Python file has a main function.

Direct run: then __name__ is set to "__main__" -> block inside will be run.

Imported Python File e.g.: import my_script then __name__ is set to my_script -> no need for main function.

How does the main function look like in other languages?

Let’s see some other programming languages:

• C++:

int main(int argc, const* argv[]) {// call of the function} // parameters can be missed

• Java:

public static void main(String[] args) {
    // Program logic goes here
}

Do we always need a main function in Python?

In Python, you don’t always need a main() function like in C, C++, or Java.

• Python runs files top to bottom.
• Any top-level code runs immediately when the script is executed.

Example: without main()

Our tool to detect main function in Python programs

How does our DetectMainFunction tool work?

Ease of Detecting main in Different languages

• Python does not require main function

• main function is an entry point in some languages: C, C++, Rust, Java

• NOTE: C++ header files are not behaving the same as import python_code!

• Function main behaves like other functions in Python

• Therefore it is harder to detect main function in Python programs

#include <iostream>
#include <vector>

std::vector<int> vec(std::vector<int> vec_int) {
  if (sizeof(vec_int) == 0) {
    std::cout << "Vector could not been found!";
  }

  for(int i: vec_int) {
    std::cout << i;
  }

  if(sizeof(vec_int) != 0) {
    return vec_int;
  }
}

std::vector<int> ints = {1,2,3,4,5,6,7,8,9,10};
vec(ints); // NOTE: Here we get a compiler error!

int main() {
  std::cout << "Only functions in main get executed in C++ or if they get called in a function that is executed in the main function!";
}

Let’s see if we can detect the main function in different scenarios 1.

Let’s see if we can detect the main function in different scenario 2.

Is it always possible to detect the main function then?

Importing Python codes

Conclusion

• It is not always possible to detect the main function in Python.
• The reason for that is Python does not require a main function like other languages.
• Static analyzers in industry are not really focusing on this “issue”.