Python中的 if __name__ == "__main__"
For Python beginners, they often see if __name__ == "__main__"it when they look at other people's code . At this time, I start to complain: "It's definitely a pretense. I don't write this sentence. The code doesn't still run well!
When I first encountered this line of code, I thought so in my heart!
Tucao returns to Tucao, there must be a reason for existence. Now let's take a look at what this code means, because this sentence can help you understand the Python module to a higher level.
Understand through examples
As long as you create a module (a .py file), the module will have a built-in attribute name generated, and the value of the module's name depends on how the module is applied. In other words, if you run the module directly, then __name__ == "__main__"; if you import a module, the value of the module name is usually the module file name.
For example, create a test1.py:
def func():
print('hello, world!')
if __name__ == "__main__":
func()In the module, the function func() is first defined to print hello, world!, and then it __name__ is judged whether it is equal __main__, if it is equal, there is printing, otherwise, the opposite is true. Now run the module and the result is:
hello, world!Description __name__ is equal to __main__ .
At this time, enter the code:
Create another test2.py:
import test1
print('bye, world!')In the module, first import test1, then print bye, world! for testing purposes, run the module, the result is:
bye, world!The operation result is only bye, world!, indicating that it is __name__ not equal to __main__.
Through the two modules of test1.py and test2.py above, we can now draw a very practical conclusion: if the module is run directly, the code block is run, and if the module is imported, the code block is not run.
