Python Main Function and Examples with Code

Last updated by Naina Batra on Aug 30, 2024 at 05:15 PM | Reading time: 7 minutes

What is Python Main Function?

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The main function is the starting point of any program. However, the Python interpreter runs the source file code in sequential order and does not call any methods that are not part of the code. However, if it is directly part of the code, it will be executed when the file is loaded as a module.

That is why there is a unique strategy for defining the main method in a Python program such that it is executed only when the program is run directly, rather than when it is imported as module.

Let's look at how to define the Python main function in a basic program. Python_main_function.py

When a Python program is executed the Python interpreter begins executing code within it. It also sets a few implicit variable values including __name__, which is set to __main__.

To execute the main function in Python we must first declare the function and then use the if __name__ == '__main__' condition.

If the Python source file has been imported as a module, the Python interpreter changes the __name__ value to the module name thus the if condition returns false and the main function is not performed.

Python allows us to use any name for the main method although it is recommended that we choose the name main(). The following code is absolutely fine but not advised.

Examples of User-Defined Copy Constructor in C++:

1. Copy Constructor for Simple Class:

2. Copy Constructor for Class with Dynamic Memory Allocation:

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‍Python Execution Modes

There are two main ways to instruct the Python interpreter to execute the code:

The most popular approach to run the file is as a Python script.

Importing the relevant code from one Python file into another. Whatever mode of execution you select, Python creates a special variable called __name__ that holds a string. And, as we previously stated, the value of this string is determined by how the code is run.

When importing from a module, you may want to know whether a specific module's function is being used as an import or whether you simply execute the module's original.py (Python script) file.

To assist with this, Python offers a built-in variable named __name__. This variable is assigned the string "__main__" depending on how you run or execute the script.

‍What is main in Python?

The Python Main Function marks the start of any Python program. When we start a program, the interpreter reads the code sequentially and does not run the main function if it has been imported as a module; however, the Main Function is only executed when it is run as a Python program.

So, if you run the script directly, Python will assign "__main__" to __name__, resulting in __name__= "__main__". (This occurs in the background. As a result, you wind up writing the conditional if statement like this:

If __name__ is "__main__":

As a result, if the conditional expression returns True, it indicates that the.py (Python Script) file is being run or processed directly. It's vital to note that if you're running something directly in the Python shell or terminal, this conditional expression is always True. As a result, programmers order the code by writing all of the relevant functional definitions at the top and then this sentence at the conclusion.

In brief, the __name__ variable allows you to determine if the file is being run directly or has been imported.

‍How To Write a Main Method In Python?

Setting up a main method in Python involves defining a function called main() that contains the code you want to execute when the script is run. Additionally, you typically use the if __name__ == "__main__": condition to ensure that the main() function is executed only when the script is run directly, not when it is imported as a module into another script.

Here's a step-by-step guide to setting up a main method in Python:

Define the main function: Create a function named main() that contains the code you want to execute when the script is run. This function can have parameters if needed.

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Use the if name == "main" condition: Place the if __name__ == "__main__": condition at the bottom of your script. This condition ensures that the main() function is executed only when the script is run directly.

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‍Add code to the main function: Inside the main() function, add the code that you want to execute when the script is run. This can include variable initialization, function calls, file I/O operations, and more.

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Execute the script: Save your Python script with a .py extension and execute it using the Python interpreter. The code inside the main() function will be executed.

python your_script.py

How to Call Main Function in Python

In Python, defining and calling the main method can be done in two ways. Let's explore both of these implementations:

1) Define in the Same File:

The first approach demonstrates defining the main method within the same file. Follow these steps to achieve this:

It's important to note that Python creates and initializes implicit variables when a program starts running. One such variable is __name__, which doesn't require a data type declaration.

During execution, the value of __name__ is set to "__main__". First, define the main() method, and then use an if condition to execute the main() method.

print("How are you?").

2) Imported from Another File:

The second approach illustrates how to define the main method when it's imported from another file.To understand this, let's first grasp the concept of modules. A module is a program imported into another file to be used multiple times without rewriting the same code.

Here are the steps:Begin by importing the module into the program file where it's going to be run.

Then, set the __name__ variable in the if condition to the name of the module (the imported module). Note that the module code will execute before the code in the file that's calling it.

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By following these approaches, you can effectively define and call the main method in Python, depending on your specific requirements.

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‍Python Main Function FAQ's

‍1) What is the Python main function used for?

The Python main function is typically used to define the entry point of a Python script. It allows you to specify the starting point of execution when the script is run as the main program.

‍2) Do I need a main function in Python?

While not strictly required, using a main function is a common convention in Python programming. It helps organize your code and makes it more modular and readable, especially for larger scripts or projects.

‍3) How do I define a main function in Python?

You can define a main function like any other function in Python, typically using the def keyword followed by the function name. Conventionally, the main function is named main().

‍4) How do I execute the main function in Python?

The main function is executed when the Python script is run as the main program. This can be achieved by using the if __name__ == "__main__": condition, which ensures that the code block under it is only executed if the script is run directly.

‍5) Can I pass arguments to the main function in Python?

Yes, you can pass arguments to the main function in Python. These arguments can be retrieved from the command line using modules like sys or argparse, allowing for more flexible and dynamic script execution.

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Naina Batra

Manager, Content Marketing

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