集合方法中“其他”一词指的是什么类型？

Question

In the help of the Built-in type set I found the word other

intersection(other, ...) set & other & ...

Return a new set with elements common to the set and all others.

My question is what are the limits of other's type, is it any iterable or any convertible to set type?

Answer 1

Read the rest of the documentation :

Note, the non-operator versions of union() , intersection() , difference() , and symmetric_difference() , issubset() , and issuperset() methods will accept any iterable as an argument . In contrast, their operator based counterparts require their arguments to be sets.

(Emphasis mine.)

Answer 2

Looking at the source (line 1236+) PyAnySet_Check is called, which checks whether other is a set , frozenset or subtype.

If this check fails, PyObject_GetIter is called with other as the argument in order to get an iterator.

So any iterable or object with an is-a relationship with set or frozenset will do.

Answer 3

It depends. For some methods, like intersection() , other can be any iterable, while for some operator based counterparts of some methods like issubset() (operator counterpart being <= ), the other has to be a set too. You can test for yourself too. Some examples here:

>>> s = set([1,2,3,4,5])
>>> s
{1, 2, 3, 4, 5}
>>> l = [1,3,5,7,9]
>>> l
[1, 3, 5, 7, 9]
>>> s.issubset(l)
False
>>> s <= l
Traceback (most recent call last):
  File "<pyshell#5>", line 1, in <module>
    s <= l
TypeError: unorderable types: set() <= list()
>>> s <= set(l)
False
>>> s.intersection(l)
{1, 3, 5}
>>>