究竟导入将在python中做什么

Question

I have written a python file a.py like this:

x = 1
def hello():
   print x

hello()

When I do import a , it is printing the value of x

Till now my understanding is import will include the variables and function definitions but why it is executing the method hello() ?

Answer 1

Python imports are not trivial, but in short, when a module gets imported, it is executed top to bottom . Since there is a call to hello, it will call the function and print hello.

For a deeper dive into imports, see:

• http://pyvideo.org/video/1707/how-import-works
• http://pyvideo.org/video/671/getting-the-most-out-of-python-imports

To be able to use a file both standalone and as a module, you can check for __name__ , which is set to __main__ , when the program runs standalone:

if __name__ == '__main__':
    hello()

See also: What does if __name__ == "__main__": do?

Answer 2

In Python, there is no clear separation between declaring and executing. In fact, there are only execution statements. For example, def hello():... is just a way to assign a function value to the module variable hello . All the statements in the module are executed in their order once the module is imported.

That's why they often use guards like:

if __name__=='__main__':
   # call hello() only when the module is run as "python module.py"
   hello()

Answer 3

你在底部调用了hello（）函数，所以当你执行“import a”时它将执行该函数！

Answer 4

you need to remove the hello() at the end, that is what is executing the function. You only want the declarations in your file a.py