a = x和a = x在Python中的区别是什么？

Question

我正在学习Python。是否有人可以帮助我了解以下两者之间的区别：VS A = X A = X [：]

Answer 1

a = x创建一个参考：

a = [2] 
x = a 
print id(a) 
print id(x) 

产地：

39727240 
39727240 

所以，如果你改变a然后x也会改变，因为它们是相同的物体

尽管

a = x[:]创建一个新对象

a = [2] 
x = a[:] 
print id(a) 
print id(x) 

产地：

41331528 
39722056 

但在这里改变a不会改变x，因为它们是不同的对象

Answer 2

In [648]: b = a 

In [649]: b[0] = 2 

In [650]: a 
Out[650]: [2] <- a also changed 

In [651]: b = a[:] <- Creating new object 

In [652]: b[0] = 3 

In [653]: b 
Out[653]: [3] 

In [654]: a 
Out[654]: [2] <- a did not change 

Answer 3

尝试t o解释：

>>> x = [1,2,3] 
>>> a = x 
>>> # a is reference to x - a[0] and x[0] are same variable 
>>> a[0] = 4 # same as x[0]... 
>>> print x # proof 
[4, 2, 3] 
>>> a = x[:] # a is copy of x 
>>> a[2] = 5 # a[2] is not x[2] 
>>> print x 
[4, 2, 3] 
>>> print a 
[4, 2, 5] 
>>>