Import a Module

import sys
sys.path.append("#path#")

path到module的上一层，不要包括module

Use a Module

import a module and use it. hehehehehe

_ __ and __init__

source：https://www.cnblogs.com/coder2012/p/4423356.html
(Oct 13 2018)

'_'

表示private

'__'

避免子类覆盖其内容
a.g.

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

I'm a method in A

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

b = B() 
b.method()

I'm a method in A

__通过改变method的名字使得子类无法修改

'__xx__'

不要调用，用于python调用

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 # 10
print num + 5 # 5
print num - 20 # 30   

if __name__=='__main__'

source：https://blog.csdn.net/yjk13703623757/article/details/77918633/
(Oct 13 2018)
当.py文件被直接运行时，if __name__=='__main__'之下的代码块将被运行；当.py文件以模块形式被导入时，if __name__ == '__main__'之下的代码块不被运行。
const.py:

PI = 3.14

def main():
    print("PI:", PI)

main()

# 运行结果：PI: 3.14

area.py:

from const import PI

def calc_round_area(radius):
    return PI * (radius ** 2)

def main():
    print("round area: ", calc_round_area(2))

main()

'''
运行结果：
PI: 3.14
round area:  12.56
'''

修改const.py

PI = 3.14

def main():
    print("PI:", PI)

if __name__ == "__main__":
    main()

运行area.py

round area: 12.56