相关知识
同级变量隐式改变
当两个变量指向同一个可变实例时，一个发生改变，另一个随之发生改变
>>> origin = []
>>> new = origin
>>> origin.append('new_value')
>>> print('origin value is: ', origin)
origin value is: ['new_value']
>>> print('while new value is: ', new)
while new value is: ['new_value']
这段代码里面，我只改变了origin的值，但是new的值也被改变了。
如何避免？
对可变类型永远使用copy
import copy
origin = []
new = copy.copy(origin)
origin.append('new_value')
print('origin value is: ', origin)
print('while new value is: ', new)
执行结果
origin value is: ['new_value']
while new value is: []
变量隐式改变指向
在同一级别的对象传递还容易被识别，但是如果是不同级别的对象传递呢？
def tricky_func(variable):
variable.append('new_value')
return variable
origin = []
new = tricky_func(origin)
print('new list should have the new_value: ', new)
print('but now the origin value also have it, which is not supposed: ', origin)
执行结果
new list should have the new_value: ['new_value']
but now the origin value also have it, which is not supposed: ['new_value']
你本希望new是一个全新的list，但是还是指向origin。非常要命的是，之后无论origin和new那个改变了值，都会引起另一个的改变。
如何避免？
调用函数的时候，使用copy之后再调用
import copy
def tricky_func(variable):
variable.append('new_value')
return variable
origin = []
new = tricky_func(copy.copy(origin))
print('new list should have the new_value: ', new)
print('now the origin is good: ', origin)
现在的执行结果
new list should have the new_value: ['new_value']
now the origin is good: []
