Main python ошибка

If you find the other answers confusing or intimidating, here’s a parable which should hopefully help. Look at the following Python program:

a = 34

When it runs, it does something: before exiting the script, Python learns that there is a variable a and that its value is the integer 34. It doesn’t do anything with this information, but it’s a complete program which does something. In order for it to produce some actual value, it needs to interact with its environment, though. What does it do with this value? It could create 34 directories, or ping the 34th server in your data center, or check the strength of the passwords of the newest 34 users in your database, or whatever; or just print something.

a = 34
print(a)

The following program is in some sense very similar to the first one.

def b():
    a = 34
    print(a)

When you run this program, it does something: Python now knows that there is a function named b, and that it doesn’t take any arguments, and that it contains some syntactically valid Python code which will be run when some other code calls it, but it doesn’t actually do anything with this code yet. In order to observe any value being produced by the code in the function, you have to actually call it:

b()

(As an aside, maybe also note that the local variable a inside the function declaration b is distinct from the global variable with the same name.)

If you are having trouble finding the cause and solution of the error NameError: name ‘main’ is not defined in Python, this article may help you. In this article, I will identify the cause of the error and perform a fix by putting name main in quotes or on the Python version you are using. Post details below.

What causes the NameError: name ‘__main__’ is not defined error?

The statements contained in a source code file are all executed by the Python interpreter as it reads the file. Python gives the variable (__name__) the value (“__main__”) when it executes the “file containing the source code” as the main program.

When the main function is called, the “if” statement is read, and a check is made to see if the __name__ variable contains the value “__main__”. Python’s “__if name __” == “__main__” function enables you to launch source code files as standalone applications or reusable modules.

The main function has two applications in the Python interpreter:

• __name__ is the module’s file name when it is used to load. If the condition in the if statement is not met, the __main__ source code will not be run.
• __name__ = __ main__ when used to run something directly. The source code in __main__ will be run if the condition in the if statement is met. 

To validate the module name, the source code uses the “if” statement when it is run.

The error NameError: name ‘__main__’ is not defined happens you don’t put name __main__ in quotes.  

Example:

def main():
  print('This is a Python tutorial for beginnners.')
  
print('Hello')

if __name__ == __main__:
    main()

Output:

Traceback (most recent call last):
 File "./prog.py", line 6, in <module>
NameError: name '__main__' is not defined

How to solve this error?

Put name __main__ in quotes.

Example:

• To fix the error NameError: name __main__ is not defined, enclose the special name __main__ in quotes.

def main():
  print('This is a Python tutorial for beginnners.')
  
print('Hello')

# Enclose the special name __main__ in quotes.
if __name__ == '__main__':
    main()

Output:

Hello
This is a Python tutorial for beginnners.

On Python 2 and Python 3 versions.

In Python 3, you can remove if__name__, and the program will still function properly.

Example:

def main():
  print('This is a Python tutorial for beginnners.')
  
print('Hello')

# Remove if__name__, and the program will still function properly.
main()

Output:

Hello
This is a Python tutorial for beginnners.

If you are still using Python 2.

Example:

def main():
  print('This is a Python tutorial for beginnners.')
  
print 'Hello'

# Enclose the special name __main__ in quotes.
if __name__ == '__main__':
    main()

Output:

Hello
This is a Python tutorial for beginnners.

Summary

I have shown the causes and given the remedies that fixed the error NameError: name ‘__main__’ is not defined in Python. This is a simple bug in Python. Remember to import it before using it. Please fix it as soon as possible. Good luck!

Python can't find '__main__' module is one of the most common errors that can occur when running a Python script. We’ll cover why this error occurs and provide two different code examples that demonstrate how it can happen. We’ll also show you how to fix the error so that you can continue developing your web applications with Python.

What is __main__ in python?

__main__ is a special name in Python that is used to indicate the source file where the program execution starts. Every Python program has a '__main__' module, and the code within that module is executed when the program is run. The '__main__' module can be located in any file, but it is typically placed in a file named ‘main.py‘.

For example, consider the following 'main.py' file:

When this program is run, the output will be as follows:

Program started!
Inside main function.
Program ended!

Why does the error occur?

There are two main reasons why the python can't find '__main__' module error might occur. The first reason is that you haven’t specified the main module in your Python script. The second reason is that your main module is not located in the same directory as your Python script. We’ll discuss each of these reasons in more detail below.

Code example 1

Let’s say you have a Python script named my_script.py and it contains the following code:

If you try to run this script, you’ll get the python can’t find ‘__main__’ module error

$ python my_script.py 
Traceback (most recent call last):
  File "my_script.py", line 7, in <module>
    some_function()
  File "my_script.py", line 4, in some_function
    print("Hello World!")
NameError: name '__main__' is not defined

This is because we haven’t specified the main module in our script. Python will look for a module named __main__ and, if it can’t find one, it will throw an error. To fix this, we need to add the main module to our script. We can do this by wrapping our code in an if __name__ == "__main__": block:

if __name__ == "__main__":
    def some_function():
        print("Hello World!")
some_function()

Now when we run our script, we get the expected output:

$ python my_script.py 
Hello World!

Code example 2

Let’s say you have a Python script named my_script.py and it contains the following code:

import some_module
def some_function():
    print("Hello World!")
some_function()



  


                       
  







  


                       
  

And you also have a Python module named some_module.py that contains the following code:

def some_other_function():
    print("Hello from some other function!")

If you try to run my_script.py, you’ll get the following error:

$ python my_script.py 
Traceback (most recent call last):
  File "my_script.py", line 7, in <module>
    import some_module
ImportError: No module named '__main__' in some_module

This is because your main module (my_script.py) is not located in the same directory as your Python script. When Python tries to import some_module, it will look for it in the current directory (the directory where my_script.py is located). Since it can’t find it there, it will throw an error. You can fix this by moving your Python script to the same directory as your main module:

    my_script.py
    some_module.py

Now when you run my_script.py, it will be able to find and import some_module.py without any problems.

As we’ve seen in the examples above, there are two ways to fix the “python can’t find ‘__main__’ module” error. The first way is to add the main module to your Python script. The second way is to move your Python script to the same directory as your main module. Below, we’ll go through both of these strategies in further depth.

Add the main module to your script

If you get this error, it means that you haven’t specified the main module in your Python script. You can fix this by wrapping your code in an if __name__ == "__main__": block:

if __name__ == "__main__":
    def some_function():
        print("Hello World!")
some_function()

When you run your script, Python will look for a module named __main__ and, if it can’t find one, it will throw an error. This block of code will ensure that Python can find your main module and avoid errors like python can't find '__main__' module

Move your script to the same directory as your main module

If you get this error, it means that your main module is not located in the same directory as your Python script. You can fix this by moving your Python script to the same directory as your main module:

my_script.py
some_module.py

When you run your Python script, it will look for modules in the current directory (the directory where my_script.py is located). By moving my_script.py to the same directory as we’re ensuring that our script can find all of the modules it needs.

Conclusion

In this article, we’ve discussed the “python can't find '__main__' module” error. We’ve seen two different code examples that demonstrate how this error can occur. And we’ve also shown you how to fix the error by either adding the main module to your script or moving your script to the same directory as your main module so that you can continue developing your web applications.

References

• StackOverflow
• Python Documentation

To learn more, also follow unittest assertraises(), prepend lists on pythonclear

Имя main в питоне не зарезервировано, просто функцию main() часто используют по аналогии с сишными программами (по этой функции видно, что делает программа и откуда всё начинается).

А ворота
if __name__ == '__main__':
нужны для того, чтобы исключить определённый код из импорта.
Каждый файл .py в питоне является модулем, его можно импортировать, как обычный модуль, и использовать содержимое из него (функции, классы и другие объекты). Но при этом и сам по себе файл что-то делает, если его запускают сам по себе. При импорте весь модуль сначала выполняется, но если тебе нужна только функция из модуля и тебе не нужно выполнять то, для чего весь этот модуль сделан, он всё равно будет выполняться весь. Поэтому в модуле ставятся ворота, которые пропускают только тогда, когда модуль запускается в виде самостоятельного файла. Когда же его импортируют, ворота не пропускают.

Зря ты начал изучение с Django, потому что там никто тебе не будет объяснять эти основы, а это реально самые основы питона.

1. Resolve the can't find '__main__' module Error in Python
2. Conclusion

In this article, we’ll discuss the error can't find '__main__' module, the causes of it, and how to resolve the error in Python.

Resolve the can't find '__main__' module Error in Python

We wrote a simple code to print in the PyCharm environment. As we see in the top right corner, the play button or running button is disabled, which means there is no way to run this code.

To be able to read this code, we need to add a configuration or add an interpreter, and then it gives us an execution. But if we click the play button, the program does not run.

The problem is that we don’t have an interpreter to run the codes on PyCharm, or we get an error when running the created interpreter. In our case, we created an interpreter, but still, the code doesn’t run.

So what caused the issue? The first reason is there is no virtual environment, and the second is the Python interpreter cannot find the project folder.

We need to check if we have installed Python on our system to resolve this issue. In the next step, we create a virtual environment for our project and specify the Python file we want to read.

To check the Python is installed or not, we open our terminal and type “python” and hit enter if you have Python installed on your system, it gives you the version of Python, and if nothing pops up, that means you do not have Python installed on our system. You need to download Python from here.

Let’s create a virtual environment for our project and create an empty folder. After that, we go to the PyCharm environment to delete the interpreter.

1. Click on the top-left corner file.
2. Go to settings. It will open up a project for you and then go to your project.
3. We click on the plus(+) button where we specifically tell the machine where we want to create our virtual environment.
4. Once the virtual environment is created, you must select it.
5. Click "OK" then "Apply".

In the next step, we will add configuration.

1. For our project, click on add configuration.
2. Click on add new and select Python.
3. After opening a new window, look at the script path where we have to select our project file, so you have to go through your project or wherever you saved your folder.
4. Once you pick up the script path or the project file, it will automatically pick up the working directory. If it doesn’t, just click on the folder, go to the project folder, and pick it up yourself.
5. Then click "Apply" and "OK".
6. We will run the code to see if everything is working fine. Click on the play button, and the code is executed successfully here.

To make it short, when you get the can't find '__main__' module error in Python. We resolve it by doing the following:

1. Adding the main module to your script.
2. Moving your script to the same directory as your main module.

Conclusion

We’ve discussed in this article how to resolve the can't find '__main__' module error in Python.