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1. Introduction to set
A collection is a 无序可变kind of container object.
The biggest feature of a collection is that the elements in the same collection are unique 不允许有重复, so the collection has its own "deduplication" effect
2. Definition of set
There are two ways to define a collection:
- Use {} for definition, this way
不能定义空集合.- Use set() to define
Example 1:
a = {
}
b = set()
print(type(a))
print(type(b))
Run the screenshot:
You can see that although the code does not report an error, the result is different. The type of a is a dictionary type, and the type of b is a collection type. This is a place that needs attention.如果想要定义一个空集合,只能使用set()的方式进行定义.
Because the elements in the collection cannot be repeated, the collection has the function of automatic deduplication.
Example 2:
# 自动去重
a = {
1, "python", 2.3, 1, "python", 2.3, 1, "python", 2.3, "python"}
print(a)
print(type(a))
# 输出结果:
# {1, 2.3, 'python'}
# <class 'set'>
The collection is unordered . Note the order of the output above, although "python" is before 2.3, but 2.3 is before "python" in the output.
集合是不支持下标索引访问Therefore collections do not have slicing operations either.
3. Collection traversal
Although the collection does not support subscript index access, it can be traversed with a for loop
Syntax: for temporary traversal in collection:
a = {
1, "python", 2.3}
for elem in a:
print(elem)
# 1
# 2.3
# python
4. Common methods of collection
Here are some common methods of collections:
| method | describe |
|---|---|
| collection.add(element) | add an element to the set |
| collection.remove(element) | Delete the specified element in the collection |
| collection.pop() | Randomly remove an element from a collection |
| Set.clear() | clear collection |
| set1.difference(set2) | Get a new set, which contains the difference set of the two sets, and the original set remains unchanged |
| set1.difference_update(set2) | Remove elements that exist in set 2 from set 1, set 1 changes, set 2 remains unchanged |
| Collection 1.union(collection 2) | Get a new collection that contains all the elements of the two collections, and the original collection remains unchanged |
| len(collection) | Count the number of elements in the collection (after deduplication) |
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