|
New in version 2.3.
The sets module provides classes for constructing and manipulating
unordered collections of unique elements. Common uses include membership testing, removing
duplicates from a sequence, and computing standard math operations on sets such as
intersection, union, difference, and symmetric difference.
Like other collections, sets support x in set, len(set),
and for x in set. Being an unordered collection, sets do
not record element position or order of insertion. Accordingly, sets do not support indexing,
slicing, or other sequence-like behavior.
Most set applications use the Set class which provides every set
method except for __hash__(). For advanced applications requiring a
hash method, the ImmutableSet class adds a __hash__()
method but omits methods which alter the contents of the set. Both Set
and ImmutableSet derive from BaseSet, an
abstract class useful for determining whether something is a set: isinstance(obj,
BaseSet).
The set classes are implemented using dictionaries. As a result, sets cannot contain
mutable elements such as lists or dictionaries. However, they can contain immutable
collections such as tuples or instances of ImmutableSet. For
convenience in implementing sets of sets, inner sets are automatically converted to immutable
form, for example, Set([Set(['dog'])]) is transformed to Set([ImmutableSet(['dog'])]).
-
- Constructs a new empty Set object. If the optional iterable
parameter is supplied, updates the set with elements obtained from iteration. All of the
elements in iterable should be immutable or be transformable to an immutable
using the protocol described in section 5.13.3.
-
| class ImmutableSet( |
[iterable]) |
- Constructs a new empty ImmutableSet object. If the optional iterable
parameter is supplied, updates the set with elements obtained from iteration. All of the
elements in iterable should be immutable or be transformable to an immutable
using the protocol described in section 5.13.3.
Because ImmutableSet objects provide a __hash__()
method, they can be used as set elements or as dictionary keys. ImmutableSet
objects do not have methods for adding or removing elements, so all of the elements must
be known when the constructor is called.
|
