A Dictionary of Python courses

Dictionary (dict)

Definition: Dictionary type in other languages, also known as map, is a type of mapping, and {key:value} unordered, its keywords must be immutable type (such as: tuple/String), in the same dictionary must be different keywords (if the same keyword, the first one will prevail)

Second, the operation

1. Create:

dic={} #创建一个空字典

dic={' Jack ': 1234, ' Tom ': 1226}

2. References and modifications:

(1) Heuristic value: Dic.get (' age ') #试探字典中是否存在age这个键, returns none if not present

(2) Display reference and modify: dic[' age ']=1238

3. Delete and clear:

(1) Delete a pair of key values: Del dic[' age '] or dic.pop (' age ')

(2) Delete entire dictionary: del dic

(3) Empty dictionary (not delete dictionary): Dic.clear ()

4. Merging dictionaries:

(1) modify directly in the original dictionary: Dic1.update (DIC2) #dic1被修改了

(2) Key value pairs of two dictionaries as new dictionaries: dict (Zip (dic1,dic2))

5. Take Keys/values/items operation:

Dic={' A ': 1, ' B ': 2}

List (Dic.keys ()) #返回key的列表

List (Dic.values ()) #返回value的列表

List (Dic.items ()) #返回键值对的列表

6. Length measurement: Len (dict) #返回的是字典的键值对个数

7. Member test: ' A ' in dic #测试键 ' A ' is in the dictionary, if it returns true

8. Traverse the dictionary:

(1) Press key to traverse:

For key in Dic.keys ():

Print (key)

(2) Traverse by value:

For value in Dic.values ():

Print (value)

(3) Key-value pair traversal:

For item in Dic.items ():

Print (item)

(4) Traversing by Element (item): #返回的是一个个键值对的元组形式

For Key,value in Dict.items ():

Print ("key=%s,value=%s"% (Key,value))

9. Dictionary Construction:

(1) Format cast: Dict ([]) or dict (a=1,b=2)

(2) Dictionary parsing: {x:x**2 for x in (2,3,4)}

10. Application of the dictionary:

(1) Nested processing of dictionaries more complex data structures

(2) Value for mapping (more powerful than arrays in C)

A Dictionary of Python courses