python下划线

双下划线

避免子类覆盖父类的方法：

class A(object):
 
 def __method(self):
 print("I'm a method in class A")

 def method_x(self):
 print("I'm another method in class A\n")

 def method(self):
 self.__method()
 self.method_x()

class B(A):
 def __method(self):
 print("I'm a method in class B")

 def method_x(self):
 print("I'm another method in class B\n")


if __name__ == '__main__':
 print("situation 1:")
 a = A()
 a.method()
 b = B()
 b.method()

 print("situation 2:")
 # a.__method()
 a._A__method()

结果：

situation 1:
I'm a method in class A
I'm another method in class A

I'm a method in class A
I'm another method in class B

situation 2:
I'm a method in class A

首尾双下划线

python内部调用，可以在自己的类中覆写操作符：

class CrazyNumber(object):
 def __init__(self, n): 
 self.n = n 
 def __add__(self, other): 
 return self.n - other 
 def __sub__(self, other): 
 return self.n + other 
 def __str__(self): 
 return str(self.n) 

num = CrazyNumber(10) 
print(num) # output is: 10
print(num + 5) # output is: 5
print(num - 20) # output is: 30