Getting started with Python-understanding

Dictionary definitions and attribute dictionaries are the only types of mappings in the Python language.

definition:{key1:value1,key2:value2}

1、键与值用冒号“：”分开；2、项与项用逗号“，”分开；

Characteristics:

1.key-value结构2.key必须可hash、且必须为不可变数据类型、必须唯一3.可存放任意多个值、可修改、可以不唯一4.无序

To Create a dictionary: person  = { "name" :  "mr.wu" ,  ‘age‘ :  18 } 或 person  = dict ({ "name" :  "mr.wu" ,  ‘age‘ :  18 })

Common operations:

• Index
• New  
        

   1  Dic_t[ " k2  " ] = 　　　　Span style= "COLOR: #800000" > " v2  2  Dict.fromkeys ([ " key1   ", "  key2   ", "  key3   "], "  value   " #   loop key list, generate a dictionary, if the following values are not assigned, all are none, if there is an assignment, the value of key is all for this string  

   

• Delete
  

  1        Dic_t.pop ("key")       # Deletes the key-value pair and returns the corresponding value2        dic_ T.popitem ()        # randomly delete 3        del dic_t["key "]      

• Modify
  1 dic_t.update (v2) # Merge two dictionaries, if the same key,list2 overrides the list key
• Enquiry
  

  1"Key"inchdic_t#Standard usage2Dic_t.get ("Key")#get Value,key does not exist then return none3dic_t["key] #获取value, key does not exist then error4Dic_t.items ()#convert key and values into a small tuple5Dic_t.setdefault ("Key","Values")#If the list has this key, it gets the value of the key, and if not, creates a key-value pair

• Key, value, key-value pairs
  

  1        Dic_t.keys ()      # print all the keys2        dic_t.value ()    # Print all the values 3        Dic_t.items ()    # Print all key-value pairs

• Cycle
  for key in dic_t: #循环key
  For key,values in Dic_t.items (): #循环键值对
• Length

enumrate ()Add an ordinal to an object that can be iterated 1 li = [11,22,33] 2 for k,v in Enumerate (LI, 1): 3 print(k,v)

Getting started with Python-understanding