[英]Python *list* "in" operator: equality, hash checking, or identity?
Those in the comments have asked me to provide my actual code, so I've removed the old example.评论中的人要求我提供我的实际代码,因此我删除了旧示例。
I'm making this , and I want two Page
s with equal titles to compare equal.我正在做这个,我希望两个具有相同标题的
Page
s 比较相等。 I've done this to the Page class:我已经对 Page 类做了这个:
def __eq__(self, other):
return self.title == other.title
but if I do this, it isn't True:但如果我这样做,那就不是真的:
>>> import mw_api_client as mwc
>>> w = mwc.Wiki('https://en.wikipedia.org/w/api.php')
>>> a = [w.page(str(i)) for i in range(20)]
>>> w.page('0') in a
False
How can I make this True?我怎样才能做到这一点?
The __contains __
method for lists is documented in the 'membership tests` section here:用于列表的
__contains __
方法记录在此处的“成员资格测试”部分:
https://docs.python.org/3.6/reference/expressions.html#membership-test-details https://docs.python.org/3.6/reference/expressions.html#membership-test-details
For container types such as list, tuple, set, frozenset, dict, or collections.deque, the expression
x in y
is equivalent toany(x is e or x == e for e in y)
.对于列表、元组、集合、冻结集、字典或 collections.deque 等容器类型
x in y
的表达式x in y
等效于any(x is e or x == e for e in y)
。
For your specific use case, you need to override __contains__
- however you can't just override __contains__
on the list - eg:对于您的特定用例,您需要覆盖
__contains__
- 但是您不能只覆盖列表中的__contains__
- 例如:
a = []
a.__contains__ = lambda: True
AttributeError: 'list' object attribute '__contains__' is read-only
The solution therefore is to create a custom class that wraps the list, and provides it's own __contains__
method.因此,解决方案是创建一个包装列表的自定义类,并提供它自己的
__contains__
方法。 Something like the following (note I'm using dicts, hence obj['title']
rather than obj.title
in this example - you might also want to test more things in __contains__
such as type comparison etc).类似于以下内容(请注意,我使用的是 dicts,因此在此示例中使用
obj['title']
而不是obj.title
- 您可能还想在__contains__
测试更多内容,例如类型比较等)。 I'm using UserList
here since it provides a nice list
class to inherit from, and makes the list contents available in data
:我在这里使用
UserList
因为它提供了一个很好的list
类来继承,并使列表内容在data
可用:
from collections import UserList
class MyList(UserList):
def __init__(self, lst):
self.data = lst
def __contains__(self, obj):
"""Return True if any item in the list has a title, and the title matches that of the passed-in dict"""
return any(obj['title'] == x['title'] for x in self.data if 'title' in x)
mr = {"title": "mr"}
mrs = {"title": "mrs"}
dr = {"title": "dr"}
random = {"foo": "bar"}
x = [mr, mrs, random]
y = MyList(x)
print(mr in y) # True
print(dr in y) # False
y.append(dr)
print(dr in y) # True
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