无法将列表转换为集合，引发“无法散列的类型:'列表'"错误 [英] Unable to convert list into set, raises "unhashable type: 'list' " error

问题描述

所以我试图找到列表的所有子列表，这就是我现在拥有的.我是Python的新手，我不明白为什么"Q3_ans = set(ans)"会引发错误.我试图将列表转换为以前设置的列表，并且可以正常工作.

So I'm trying to find all sub-lists of a list and here is what I have now. I'm new to Python and I don't understand why " Q3_ans=set(ans)" raises an error. I've tried to convert a list to set before and it works.

def f2(seq):
    '''
    This is the base case of the recursion from function all_sublists
    '''
    assert len(seq)==2
    assert isinstance(x,list)
    a,b=seq
    return [[a],[b],[a,b]]


def all_sublists(x):
    '''
    This function will generate all of the sublists of a list, not including the empty one, using recursion
    '''
    assert isinstance(x,list)
    ans=[]
    for i in range(0,len(x)-1):
        for j in range(1,len(x)):
            temp=[x[i],x[j]]
            temp=[f2(temp)]
            ans.extend(temp)
    Q3_ans=set(ans) 
    return Q3_ans

这是我运行代码时的错误 y = [1,2,3,4,5]

Here is the error when I run my code y=[1,2,3,4,5]

all_sublists(y)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-108-f8b1bb0a7001> in <module>
----> 1 all_sublists(y)

<ipython-input-106-84f4f752e98e> in all_sublists(x)
     10             temp=[f2(temp)]
     11             ans.extend(temp)
---> 12     Q3_ans=set(ans)
     13     return Q3_ans

TypeError: unhashable type: 'list'

推荐答案

这是问题的本质:

>>> set([[["a"],["b"],["a","b"]]])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: 'list'

那是什么意思?

set([iterable])

返回一个新的set对象，该对象的元素均来自于iterable. 集合中的元素必须是可散列的.

可哈希

如果对象具有从不改变的哈希值，则该对象是可哈希的 在其生命周期内(需要使用__hash__()方法)，并且可以 与其他对象相比(它需要一个__eq__()方法).可散列 比较相等的对象必须具有相同的哈希值.

An object is hashable if it has a hash value which never changes during its lifetime (it needs a __hash__() method), and can be compared to other objects (it needs an __eq__() method). Hashable objects which compare equal must have the same hash value.

可哈希性使对象可用作字典键和集合 成员，因为这些数据结构在内部使用哈希值.

Hashability makes an object usable as a dictionary key and a set member, because these data structures use the hash value internally.

Python的所有不可变内置对象都是可哈希的； 可变 容器(例如列表或词典)不是.

All of Python’s immutable built-in objects are hashable; mutable containers (such as lists or dictionaries) are not.

此处的关键字是 可变

The keywords here are mutable

可变对象可以更改其值，但保留其id().

Mutable objects can change their value but keep their id().

和 不可变

具有固定值的对象.不可变的对象包括数字， 字符串和元组.这样的对象不能改变.有一个新对象 如果必须存储其他值，则创建该属性.他们玩 在需要恒定哈希值的地方起着重要的作用 例如作为字典中的键.

An object with a fixed value. Immutable objects include numbers, strings and tuples. Such an object cannot be altered. A new object has to be created if a different value has to be stored. They play an important role in places where a constant hash value is needed, for example as a key in a dictionary.

因此，不能将list用作set元素. tuple可以工作:

So, you can't use a list as set element. A tuple would work:

>>> set([(("a"),("b"),("a","b"))])
{('a', 'b', ('a', 'b'))}

这篇关于无法将列表转换为集合，引发“无法散列的类型:'列表'"错误的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！