Question

>>> AB
['1', '3', '1', '3']
>>> BC = AB
>>> BC
['1', '3', '1', '3']
>>> BC.sort()
>>> BC
['1', '1', '3', '3']
>>> AB
['1', '1', '3', '3']

我想排序只列出BC。为什么它也排序列表AB以及如何防止它？

Answer 1

你基本上用AB和BC指向程序内存中的相同区域。因此，要将BC创建为新列表，并将其保存在内存中的其他位置，您可以执行以下操作：

假设这是python：

BC = AB[:]  # creates a copy of AB

现在，当你修改BC时，它不会改变AB。这样排序对AB没有影响。现在他们指向记忆中的不同位置。

Answer 2

BC和AB可能指向到内存中的相同对象，变量持有者AB和BC就像指针。它们都指向到同一个东西，所以如果你对BC进行排序，BC列表指向进行排序，AB也指向现在排序列出BC。

要更正此问题，您可以说BC = AB[:]而不是说Unhandled exception in thread started by <function wrapper at 0x1071c11b8> Traceback (most recent call last): File "/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/django/utils/autoreload.py", line 93, in wrapper fn(*args, **kwargs) File "/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 101, in inner_run self.validate(display_num_errors=True) File "/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/django/core/management/base.py", line 310, in validate num_errors = get_validation_errors(s, app) File "/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/django/core/management/validation.py", line 34, in get_validation_errors for (app_name, error) in get_app_errors().items(): File "/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/django/db/models/loading.py", line 196, in get_app_errors self._populate() File "/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/django/db/models/loading.py", line 78, in _populate self.load_app(app_name) File "/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/django/db/models/loading.py", line 99, in load_app models = import_module('%s.models' % app_name) File "/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/django/utils/importlib.py", line 40, in import_module __import__(name) File "/Users/shivakrishna/shiva/app/post-web-1.6/modes/directory/models.py", line 24, in <module> from PIL import Image, ImageDraw, ImageFont File "/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/PIL/Image.py", line 67, in <module> from PIL import _imaging as core ImportError: dlopen(/Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/PIL/_imaging.so, 2): Library not loaded: /opt/local/lib/libjpeg.9.dylib Referenced from: /Users/shivakrishna/.virtualenvs/project/lib/python2.7/site-packages/PIL/_imaging.so Reason: image not found，而不是AB本身，它会在BC中存储AB的副本。这将导致：对一个不的更改反映在另一个

中。

如何将sort（）限制为一个列表？

2 个答案: