This is the sixth day of my participation in the August More text Challenge. For details, see:August is more challenging

A set is an unordered sequence of elements that do not repeat

You can create a collection using curly braces {} or the set() function

To create an empty set, you must use set() instead of {}, because {} is used to create an empty dictionary

Collections and dictionaries are mutable types!! Previously, lists were mutable, strings and tuples immutable.

1. Getting to know the group

The advantages of Python collections

Since the elements in a set cannot appear more than once, this makes it largely efficient to remove duplicate values from a list or tuple, and to perform common mathematical operations such as union fetching and intersection fetching.

Hash types are collections and dictionaries

Note: Collections do not have index, slice, repeat, join properties, collections only member operators, iterated loop traversal, enumeration properties!

  1. Features: Mutable elements cannot be added to a set. (E.g., list)

A set is an unordered sequence of elements that does not repeat. You can create a collection using curly braces {} or the set() function. A = {1,2,3,45,12324} set(a)

Note: when creating an empty set, you can’t use a = {}. This is an empty dictionary. You should use set() instead.

Have intersection, union, difference set……

2. & common parts;

And sets: | all parts;

Difference set: – subtracts the shared part, keeping the value in the first original set.

(1) {}

Note: (Sets will automatically de-weight)

a = {'a','bb','yy','a','fg'} 
print(a)
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Output: {‘ a ‘, ‘bb’, ‘yy’, ‘fg’}

Extension: Quickly determine if an element is in a set. Use the in.

    print('bb' in a)
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If True, yes, False, no.

(2) set ()

    a = set('whuhan')
    b = set('zhangxinyi')
    print(a)     
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The output is: {‘a’,’h’,’n’,’u’,’w’} unordered to repeat

Purpose: Set () can be used when deduplicating elements

2. Basic operations of the set:

  1. Note: Add must be added one at a time.

Collection: Unordered data types

The order of addition is not the same as the order of storage in the collection

    a = {'a','bb','yy','fg'}
    a.add('zhangxinyi')
    print(a)     
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{‘zhangxinyi’,’yy’,’bb’,’a’,’fg’}

  1. Remove elements

(1)remove: delete

a = {'a','bb','yy','fg'}
a.remove('bb')    
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Output: {‘yy’,’a’,’fg’}

(2) Pop random deletion

a.pop()   
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Randomly deletes a value from the collection

  1. Change the update

    S = {1, 2, 3, 4, 5} s.u pdate (‘ wuhan)

Output: {‘w’,’1′,’a’,’2′,’h’,’3′,’u’,’5′,’n’,’4′}

  1. check

(1) Judge whether there is no intersection, if there is no intersection, the judgment is correct, otherwise error isdisjoint

S1 = {1,2,3} s2 = {3,4,5} s1.isdisjoint (s2)Copy the code

The output is False

(2) Determine whether set S1 is a subset of S2. If yes, output True; otherwise, output False

s1.issubset(s2)  
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The output is False

S1. issuperset(s2)

s1.issuperset(s2)  
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The output is False

Count the number of elements in the set

a = {'a','bb','yy','fg'}
b = set(a)
print(len(b))  
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The output is 4

A = [12,5,3,2,33], for example: if len(a)<=2:

  1. Clear () clear()

     a = {'a','bb','yy','fg'}
 a.clear()
 print(a)        
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Output: set()

It’s important to remember that one major drawback to immutable sets is that since they’re immutable, this means you can’t add elements to them or remove elements from them!

2. Trimesh operations: (can optimize the code)

In computer languages, there is an expression called a triadic operation, also known as a ternary expression. Basic expression: variable = value 1 if condition else value 2 If condition is met, variable is valued at 1; Otherwise, the value is 2.

Example 1:

If a>b else b = a; if a>b else B = a; Otherwise, c is equal to b.Copy the code

Example 2:

    a = 10
    if a > 5:
            print(True)
    else:
            print(False)
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Convert to a trimesh operation expression:

    print(True if a > 5 else False)  
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Print True if a > 5, False otherwise