CODEWITHSUNDEEP
pythonset
planetp
planetp

Reputation: 16065

Why do set operations work with iterables only when using methods?

Why do set operations work with arbitrary iterables when using set methods, but not operators? To show what I mean:

>>> {0, 1, 2, 3}.intersection([0, 1])
{0, 1}
>>> {0, 1, 2, 3} & [0, 1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for &: 'set' and 'list'
>>>
>>> {0, 1, 2, 3}.union([4, 5])
{0, 1, 2, 3, 4, 5}
>>> {0, 1, 2, 3} | [4, 5]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for |: 'set' and 'list'

Upvotes: 2

Views: 83

Answers (1)

user2357112
user2357112

Reputation: 280291

From the docs:

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. This precludes error-prone constructions like set('abc') & 'cbs' in favor of the more readable set('abc').intersection('cbs').

It was considered less error-prone this way.

Upvotes: 7

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