[英]Adding frozenset to set of other frozensets
I am trying to add a frozenset to an already existing set of frozensets however when i try to use the add() function to add it the return is None.我正在尝试将一个frozenset 添加到一个已经存在的frozensets 中,但是当我尝试使用add() 函数来添加它时,返回是None。 I tried using the update() function instead but to no avail.我尝试使用 update() 函数,但无济于事。 I am forced to use frozensets because I need a set of sets and this seems like the only solution in Python.我被迫使用frozensets,因为我需要一组集合,这似乎是Python 中唯一的解决方案。 The literal is just a list of one element of type String.文字只是一个字符串类型元素的列表。
print(literal)
print(clauses)
clauses = clauses.add(frozenset(literal))
print(clauses)
The output looks like this:输出如下所示:
['!y']
{frozenset({'!y', 'z', 'x'})}
None
The general rule ( https://docs.python.org/3/library/stdtypes.html )一般规则( https://docs.python.org/3/library/stdtypes.html )
The methods that add, subtract, or rearrange their members in place, and don't return a specific item, never return the collection instance itself but None.添加、减去或重新排列其成员的方法,并且不返回特定项,从不返回集合实例本身而是 None。
That's why:这就是为什么:
clauses = clauses.add(frozenset(literal))
means:方法:
clauses.add(frozenset(literal))
clauses = None
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