Collection type (set) learning summary in Python

Set is an unordered set of elements, which supports mathematical operations such as union, intersection, difference and symmetry difference. However, since set does not record the position of elements, it does not support the operations of index, shard and other sequences.

Initialize the

s0 = set()

d0 = {}

s1 = {0}

s2 = {i % 2 for i in range(10)}

s = set('hi')

t = set(['h', 'e', 'l', 'l', 'o'])

print(s0, s1, s2, s, t, type(d0))

Operation results:

set() {0} {0, 1} {'i', 'h'} {'e', 'o', 'l', 'h'} <class 'dict'>

prompt
1. S0, d0: the use of {} can only create an empty dictionary, the creation of an empty set must use set();
2. The elements in ss, sl: set are unordered and unrepeated, which can be used to remove the repeated elements in the list.

Arithmetic operations

print(s.intersection(t), s & t)  #  intersection 

print(s.union(t), s | t)   #  And set  

print(s.difference(t), s - t)  #  Difference set  

print(s.symmetric_difference(t), s ^ t) #  Symmetric difference set  

print(s1.issubset(s2), s1 <= s2) #  A subset of 

print(s1.issuperset(s2), s1 >= s2)      #  contains 

Operation results:

{'h'} {'h'}

{'l', 'h', 'i', 'o', 'e'} {'l', 'h', 'i', 'o', 'e'}

{'i'} {'i'}

{'i', 'l', 'o', 'e'} {'i', 'l', 'o', 'e'}

True True

False False

prompt
1. Non-operator methods accept any iterable object as a parameter, such as s.date ([0, 1]);
2. Other equivalent operations: s.date (t) and s |= t, s & s tersection_update(t) and s &= t, s.fference_update (t) and s -= t, s.s.mmetric_difference_update (t) and s ^= t, etc.

Basic method

s = {0}

print(s, len(s))   #  Gets the total number of elements in the collection 

s.add("x")         #  Add an element 

print(s)

s.update([1,2,3])  #  Add multiple elements 

print(s, "x" in s) #  Membership test 

s.remove("x")      #  Get rid of an element 

print(s, "x" not in s)  

s.discard("x")     #  Deletes the specified element if it exists in the collection 

c = s.copy()       #  Copying collection      

print(s, s.pop())  #  An uncertain element in the pop-up collection, thrown if the original set is empty  KeyError

s.clear()          #  Delete the elements in the collection 

print(s, c)

Operation results:

{0} 1

{0, 'x'}

{0, 'x', 1, 2, 3} True

{0, 1, 2, 3} True

{1, 2, 3} 0

set() {0, 1, 2, 3}