python - 列表比较失败

Question

出于某种原因，我让列表始终相等，即使在打印时，您可以看到它们并不总是相等。

当 previous_list = [1,0,0,0,0] 和 current_list = [0,0,0,0,0] 时返回 True

有很多关于比较列表的问题，但我尝试了很多不同的答案，比如 cmp()，但它也返回 0。那为什么明明说一样，打印出来却发现不一样呢？

while True:
    previous_status_list = current_status_list
    print str(previous_status_list) + " PREVIOUS"
    if door_status == 'closed' and status_for_loop == 'closed':
        overall_status_list[0] = 0
    else:
        overall_status_list[0] = 1
    if door_locked_status == False:
        overall_status_list[1] = 0
    else:
        overall_status_list[1] = 1
    if door_breached_status == False:
        overall_status_list[2] = 0
    else:
        overall_status_list[2] = 1
    if door_propped_status == False:
        overall_status_list[3] = 0
    else:
        overall_status_list[3] = 1
    if egress_status == False:
        overall_status_list[4] = 0
    else:
        overall_status_list[4] = 1
    current_status_list = overall_status_list
    if current_status_list == previous_status_list:
        print 'TRUE'
    else:
        print 'False'
    print str(current_status_list)  + " CURRENT"
    sleeptime.sleep(3)

Answer 1

您没有比较两个不同的列表，因为您没有制作副本:

previous_status_list = current_status_list

previous_status_list 和 current_status_list 引用相同的对象。通过一个引用改变列表会改变另一个:

改为创建(浅)副本:

previous_status_list = current_status_list[:]

演示:

>>> current_status_list = ['foo', 'bar', 'baz']
>>> previous_status_list = current_status_list
>>> current_status_list is previous_status_list
True
>>> current_status_list.append('spam')
>>> previous_status_list
['foo', 'bar', 'baz', 'spam']
>>> previous_status_list = current_status_list[:]  # shallow copy
>>> current_status_list is previous_status_list
False
>>> current_status_list.append('ham')
>>> current_status_list
['foo', 'bar', 'baz', 'spam', 'ham']
>>> previous_status_list
['foo', 'bar', 'baz', 'spam']

请注意 is 标识运算符如何显示这两个名称指的是同一个对象，直到创建了一个副本。此外，通过 current_status_list 对列表所做的更改会显示在 previous_status_list 中，直到创建副本为止。