The following is the most common pattern that trips people up.
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if __name__ == '__main__': # some logic here |
Every Python module defines a variable called __name__. It can either contain module name or __main__ depending upon how a module is executed.
We can execute a Python file (or module) in two ways:
- Using the
importstatement. - As the main module by passing module name to the Python interpreter (i.e
python module_name.py).
If a module is imported inside another module, then the __name__ variable in the imported module refers to the module name. On the other hand, if a module is executed as the main module (i.e. module which starts the program), then the __name__ variable contains __main__.
This pattern helps us to execute some logic only when the module is run as the main module.
my_server.py
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def start_server(): # logic to start the server print("Server started") if __name__ == '__main__': start_server() |
Output:
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python my_server.py Server started |
In this example, we are able to call start_server() function because we are running my_server.py as the main module. Now let’s see what would happen if we import our main module inside another module.
utils.py
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import my_server print("utils.py executed") |
Output:
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python utils.py utils.py executed |
As you can see, this time the start_server() function from my_server.py module is not called because we are not executing my_server.py as the main module.
