Python Set

#python #datastructure #programming #language #efficiency

They are two types of sets: set and frozenset
- set: Not hashable, cannot be nested
- frozenset: Hashable, we can have frozenset inside set
Take a look on both codes below

found = len(needles & haystack) # (1)

found = 0 # (2)
for n in needless:
	if n in haystack:
		found += 1

The code (1) has superior performance than the code (2).
To build a set

>>> s = {1} # faster than
>>> s = set([1,2,3])

Take a look on [[n803-setcomp]]#
Elements inside set need to be [[nxj2-hashable]] or has the methods __hash__ and __eq__
- But the check of existence of element is fast
Sets have memory overhead
Sorting is not guaranteed in set, adding elements can change the order
[[9n4u-python-dictionary]] methods like keys() and items() implement some set methods like: &, |, - and ^.