Question

为什么不能使用子集运算符＆lt; =？来比较集合和ImmutableSet？例如。运行以下代码。这有什么问题？任何帮助赞赏。我正在使用Python 2.7。

>>> from sets import ImmutableSet
>>> X = ImmutableSet([1,2,3])
>>> X <= set([1,2,3,4])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/sets.py", line 291, in issubset
    self._binary_sanity_check(other)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/sets.py", line 328, in _binary_sanity_check
    raise TypeError, "Binary operation only permitted between sets"
TypeError: Binary operation only permitted between sets
>>>

Answer 1

使用frozenset object代替; sets module已被弃用，与内置类型无法比较：

>>> X = frozenset([1,2,3])
>>> X <= set([1,2,3,4])
True

来自sets模块的文档：

自2.6版开始不推荐使用：内置的set / frozenset类型取代了此模块。

如果您使用sets模块遇到代码，请在比较时专门使用其类型：

>>> from sets import Set, ImmutableSet
>>> Set([1, 2, 3]) <= set([1, 2, 3, 4])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mj/Development/Libraries/buildout.python/parts/opt/lib/python2.7/sets.py", line 291, in issubset
    self._binary_sanity_check(other)
  File "/Users/mj/Development/Libraries/buildout.python/parts/opt/lib/python2.7/sets.py", line 328, in _binary_sanity_check
    raise TypeError, "Binary operation only permitted between sets"
TypeError: Binary operation only permitted between sets
>>> ImmutableSet([1, 2, 3]) <= Set([1, 2, 3, 4])
True

Python set和frozenset确实接受了许多运算符和函数的任何序列，因此反转您的测试也有效：

>>> X
frozenset([1, 2, 3])
>>> set([1,2,3,4]) >= X
True

这同样适用于.issubset()和sets.ImmutableSet类的sets.Set功能：

>>> X.issubset(set([1,2,3,4]))
True

但不要混用已弃用的类型和新的内置函数完全是最佳选择。

为什么我不能比较python 2.7中的set和immutableset

1 个答案: