Instead of this:
a = {"foo": None, "bar": None}
Is there a way to write this?
b = {"foo", "bar"}
And still let b have constant time access (i.e. not a Python set, which cannot be keyed into)?
3 Answers
Actually, in Python 2.7 and 3.2+, this really does work:
>>> b = {"foo", "bar"}
>>> b
set(['foo', 'bar'])
You can't use [] access on a set ("key into"), but you can test for inclusion:
>>> 'x' in b
False
>>> 'foo' in b
True
Sets are as close to value-less dictionaries as it gets. They have average-case constant-time access, require hashable objects (i.e. no storing lists or dicts in sets), and even support their own comprehension syntax:
{x**2 for x in xrange(100)}
Yes, sets:
set() -> new empty set object
set(iterable) -> new set object
Build an unordered collection of unique elements.
Related: How is set() implemented?
Time complexity :
In order to "key" into a set in constant time use in:
>>> s = set(['foo', 'bar', 'baz'])
>>> 'foo' in s
True
>>> 'fork' in s
False
