在很多Python代码中,最后的部分会执行一个判断语句(注意__name__中下划线的长度,它表示:两根下划线+name+两根下划线)
if __name__== '__main__':
那么这个判断的代码是什么意思?
在Python编译器读取源文件的时候会执行它找到的所有代码,而在执行之前会根据当前运行的模块是否为主程序而定义变量__name__的值是__main__还是模块名。因此,该判断语句为真的时候,说明当前运行的脚本为主程序,而非主程序所引用的一个模块。当你想要运行一些只有在模块当做程序运行时,只要将代码放在 if __name__=="__main__": 判断语句之后就可以了。
举例说明:
file_one.py文件
#下面一行为环境变量,指明python.exe的目录
#!C:\Program Files\Python\python.exe
# -*- coding: UTF-8 -*-
def func():
print("func() in one.py")
print("top-level in one.py")
if __name__ =="__main__":
print("one.py is being run directly")
else:
print("one.py is being imported into another module")
运行结果:
"C:\Program Files\Python\python.exe" E:/python_phcharm/file_one.py
top-level in one.py
one.py is being run directly
file_two.py文件
#下面一行为环境变量,指明python.exe的目录
#!C:\Program Files\Python\python.exe
# -*- coding: UTF-8 -*-
import file_one #start executing one.py
print("top-level in two.py")
file_one.func()
if __name__=="__main__":
print("two.py is being run directly")
else:
print("two.py is being import into another module")
运行结果:
"C:\Program Files\Python\python.exe" E:/python_phcharm/file_two.py
top-level in one.py
one.py is being imported into another module
top-level in two.py
func() in one.py
two.py is being run directly