ch02

ch02/sets.py

@@ -0,0 +1,51 @@
+# sets.py
+
+
+>>> small_primes = set()  # empty set
+>>> small_primes.add(2)  # adding one element at a time
+>>> small_primes.add(3)
+>>> small_primes.add(5)
+>>> small_primes
+{2, 3, 5}
+>>> small_primes.add(1)  # Look what I've done, 1 is not a prime!
+>>> small_primes
+{1, 2, 3, 5}
+>>> small_primes.remove(1)  # so let's remove it
+>>> 3 in small_primes  # membership test
+True
+>>> 4 in small_primes
+False
+>>> 4 not in small_primes  # negated membership test
+True
+>>> small_primes.add(3)  # trying to add 3 again
+>>> small_primes
+{2, 3, 5}  # no change, duplication is not allowed
+>>> bigger_primes = set([5, 7, 11, 13])  # faster creation
+>>> small_primes | bigger_primes  # union operator `|`
+{2, 3, 5, 7, 11, 13}
+>>> small_primes & bigger_primes  # intersection operator `&`
+{5}
+>>> small_primes - bigger_primes  # difference operator `-`
+{2, 3}
+
+
+>>> small_primes = {2, 3, 5, 5, 3}
+>>> small_primes
+{2, 3, 5}
+
+
+
+
+# frozenset
+>>> small_primes = frozenset([2, 3, 5, 7])
+>>> bigger_primes = frozenset([5, 7, 11])
+>>> small_primes.add(11)  # we cannot add to a frozenset
+Traceback (most recent call last):
+  File "<stdin>", line 1, in <module>
+AttributeError: 'frozenset' object has no attribute 'add'
+>>> small_primes.remove(2)  # neither we can remove
+Traceback (most recent call last):
+  File "<stdin>", line 1, in <module>
+AttributeError: 'frozenset' object has no attribute 'remove'
+>>> small_primes & bigger_primes  # intersect, union, etc. allowed
+frozenset({5, 7})