Core Python Programming (2nd Edition)

7.8. Built-in Functions

7.8.1. Standard Type Functions

len()

The len() BIF for sets returns cardinality (or the number of elements) of the set passed in as the argument.

>>> s = set(u) >>> s set(['p', 'c', 'e', 'h', 's', 'o']) >>> len(s) 6

7.8.2. Set Type Factory Functions

set() and frozenset()

The set() and frozenset() factory functions generate mutable and immutable sets, respectively. If no argument is provided, then an empty set is created. If one is provided, it must be an iterable, i.e., a sequence, an iterator, or an object that supports iteration such as a file or a dictionary.

>>> set() set([]) >>> set([]) set([]) >>> set(()) set([]) >>> set('shop') set(['h', 's', 'o', 'p']) >>> >>> frozenset(['foo', 'bar']) frozenset(['foo', 'bar']) >>> >>> f = open('numbers', 'w') >>> for i in range(5): ... f.write('%d\n' % i) ... >>> f.close() >>> f = open('numbers', 'r') >>> set(f) set(['0\n', '3\n', '1\n', '4\n', '2\n']) >>> f.close()