dictionary
Explanation:
- Dictionaries and lists are the same as a worthy collection;
- Dictionary Index not like that list must be an integer, a dictionary index can be of many types;
- Index dictionary is called "button", and the value of the key associated with the key together referred to as "key-value" pairs.
grammar:
{"key1":value,"key2":value,....}或者{'key1':value,'key2':value,....}
Example:
>>> mydic={'name':'bobo','age':12,'bobby':'apple'}
>>> mydic
{'name': 'bobo', 'age': 12, 'bobby': 'apple'}
>>> mydic['age']
12
>>> complexdic={'id':1,'content':mydic,'range':10}
>>> complexdic
{'id': 1, 'content': {'name': 'bobo', 'age': 12, 'bobby': 'apple'}, 'range': 10}
>>> complexdic['content']
{'name': 'bobo', 'age': 12, 'bobby': 'apple'}
>>> complexdic['content']['name']
'bobo'
Description: dictionaries and lists by index value, dict [ 'keys']; type value corresponding to the key dictionary may also be a dictionary.
Dictionary and list:
Dictionary key-value pair is not stored in the order, so long as the number of key-value pairs, as the content, then the two are equal dictionaries
Example:
>>> mydic {'name': 'bobo', 'age': 12, 'bobby': 'apple'} >>> mydd={'name':'bobo',"bobby":'apple',"age":12} >>> mydd {'name': 'bobo', 'bobby': 'apple', 'age': 12} >>> mydd==mydic True >>> mylis=[1,2,3] >>> mylis [1, 2, 3] >>> myll=[1,3,2] >>> myll [1, 3, 2] >>>=='re wrong Mylla False
Description: The dictionary is not stored in the order of the list is stored sequentially. Dictionary-slice images as a list.
Dictionary traversal methods:
keys (), values (), items (): Get all available keys, respectively, to obtain an overview of all values, fetch all keys (this value is tuple)
Example:
>>> mydic {'name': 'bobo', 'age': 12, 'bobby': 'apple'} >>> mydic.keys() dict_keys(['name', 'age', 'bobby']) >>> for x in mydic.keys(): ... print(x) ... name age bobby >>> for x in mydic.values(): ... print(x) ... bobo 12 apple >>> for x,y in mydic.items(): ... print(x,y) ... name bobo age 12 bobby apple
Check dictionary key, the value of the presence of
Note: Before accessing the value of a key, the key to determine whether there is important in the dictionary.
get () method:
Two parameters, a first name is a bond; a second predetermined value; when the key corresponding to the key value does not exist or do not exist, we can return to the specified value.
Example:
>>> mydic {'name': 'bobo', 'age': 12, 'bobby': 'apple'} >>> key_value=mydic.get('adress',-1) >>> key_value -1 >>> key_value1=mydic.get('name','不存在') >>> key_value1 'bobo'
Description: When there is a value corresponding to the key, get returns the value corresponding to the key in the dictionary; if there is no will return the value specified by us
setDefault () Method:
When faced with a key to set a default value, setdefault () method will be very convenient. It is built-checking mechanism to help us determine whether the key is a good solution to the problems.
Example 1: We do not have setdefault (practices when):
>>> mydic {'name': 'bobo', 'age': 12, 'bobby': 'apple'} >>> if 'color' in mydic: ... pass ... else: ... mydic['color']='yellow' ... >>> mydic {'name': 'bobo', 'age': 12, 'bobby': 'apple', 'color': 'yellow'}
Example 2: When the setDefault () Method:
>>> mydic {'name': 'bobo', 'age': 12, 'bobby': 'apple', 'color': 'yellow'} >>> mydic.setdefault('adress','china') 'china' >>> mydic {'name': 'bobo', 'age': 12, 'bobby': 'apple', 'color': 'yellow', 'adress': 'china'} >>> mydic.setdefault('adress','usa') 'china' >>> mydic {'name': 'bobo', 'age': 12, 'bobby': 'apple', 'color': 'yellow', 'adress': 'china'}
Description: setdefault () method to check the value corresponding to the key not, adds the key to the dictionary, and we set the default value specified. When the discovery key has a value corresponding to the keys will not re-assign the corresponding value.
Example 3: give you a bunch of strings, requires you to be able to calculate each character appears several times in a string?
Ideas: Character - the number of times, which is obviously want us to use a dictionary expensive. As a key character - the number of times as the value.
Example:
= myStr ' alsjdnwlsdisla ' count_dic = {} for Item in myStr: count_dic.setdefault (Item, 0 ) # key added to give the dictionary to prevent the key being given to the set value count_dic [Item] = [Item] count_dic + . 1 # by assigning an index value to the index number corresponding to each iteration plus a print (count_dic)
Output:
{'a': 2, 'l': 3, 's': 3, 'j': 1, 'd': 2, 'n': 1, 'w': 1, 'i': 1}