python dict comprehension

shallow copy of a dictionaryDict.setdefault (Key, Default=none): Similar to get (), but if the key does not already exist in the dictionary, the key will be added and the value will be set to defaultCompared with list, Dict has the following features: The speed of finding and inserting is very fast and will not increase with the increase of key; It takes a lot of memory, and it wastes a lot of memory. And the list is the opposite:

value:defsort_by_value (d): Items=d.items () Backitems=[[v[1],v[0]] forVinchItems]backitems.sort ()return[backitems[i][1] forIinchRange (0,len (backitems))]#or a line to fix:[v forVinchSorted (di.values ())]#use lambda expressions to sort and be more flexible:Sorted (d.items (),Lambdax, y:cmp (x[1], y[1]), or reverse order: sorted (d.items (),Lambdax, y:cmp (x[1], y[1]), reverse=True)#Sort by the key= parameter of the sorted function:#Sort by KeyPrintSorted (dict1.items (), key=Lambdad:d[0])#So

# result is a dictionary that removes attribute values that are none for inch Result: if not Result[key]: del Result[key] Continue But the error message is as followsRuntimeerror:dictionary changed size during iteration #This error is thrown when Python iterates through a dict, set type, and changes the length of the variable or side-by-side modification.After

can only do small to large sorting of numeric lists.Example:A = [13,12,23,43,55,6,4545,2]A.sort ()Print (a)######### #dict字典方法# # #fromkeys to create a dictionary from a sequence and specify a uniform valueExample:v = Dict.fromkeys (["ASD", 234,3333,2323],555)Print (v)# # #get Print out the value of key in the dictionaryExample:info = {"K1": 3, "K2": 4, "K3": 5, "K4": 6, "K5": 7}v = info.get ("K1") # # #get ("ASD", 1111) when a key ASD does not exist

Example:d={ ‘name‘:‘yy‘}Key value judgmentd.has_key(‘name‘) #如果有key返回Trued.get(‘name‘) #如果没有key返回NoneAdd and update#赋值可以是字符，数字，列表，元组，字典。d[‘age‘] = 28d[‘friends‘] = [‘john‘,‘megan‘,‘alex‘]Deletedel d[‘name‘] #删除指定keyd.clear() #清空字典Take value Gets the value of the specified key d[‘name‘] 如果‘name‘这个key不存在，会抛出异常可以替换为：d.get(‘name‘,‘yy‘) #如果没有‘name‘这个key，则赋予默认值‘yy‘也可以先判断是否存在这个key:d.has_key(‘name‘) #返回true或falseTraverse Dictionary Traversing key and valuefor k,v in d.

In the Python manual:Sorted (Iterable[,cmp,[,key[,reverse=true]])Function: Return a new sorted list from the items in iterable.The first parameter is a iterable, and the return value is a list that sorts the elements in iterable. The optional parameters are three, CMP, key, and reverse. 1) CMP Specifies a custom comparison function that receives two parameters (elements of iterable), returns a negative number if the first argument is less than the sec

This paper deeply analyzes the application of dict,set,list,tuple in Python and its corresponding example, which helps readers to master the concept and principle. Specifically as follows: 1. Dictionary (dict) Dict surrounded by {}Dict.keys (), Dict.values (), Dict.items ()Hash (obj) returns the hashed value of obj i

The examples in this article describe the way Python uses dictionary dict to determine whether a specified key value exists. Share to everyone for your reference. Specific as follows: There are two methods in Python to determine whether a specified key value exists, one is judged by the method of the Dictionary object, and the other is through the in method, th

generally not used for list () and tuple (). more cases, They are used for Xuan exchange between two types, such as you need to convert an existing tuple into a list type (then you can modify its elements), or vice versa.alist=[' 123 ', ' 456 '];Atuple=tuple (alist);Print Atuple>>> (' 123 ', ' 456 ')Alist==atuple>>> FalseAlist2=list (Atuple)Alist2==alist>>>trueAlist is Alist2>>>falseAgain ID () confirm, [ID (x) for x in Alist,atuple,alist2]>>>[10903800,12003900,11730280]So either list () or tup

, for large lists, the extend executes faster. Python supports the + = operator.Li + = [' both '] is equivalent to li.extend ([' both ']). The + = operator can be used for lists, strings, and integers, and it can also be overloaded for user-defined classes. The * operator can act as a repeating device on the list. Li = [1, 2] * 3 equals to li = [1, 2] + [1, 2] + [1, 2], and three lists are connected as one. Touple　　 A tuple is an

This example describes how Python can determine whether a specified key value exists through a dictionary dict. Share to everyone for your reference. Specifically as follows: There are two ways in Python to determine whether a specified key value exists, one that is has_key by the method of the Dictionary object, the other is through the in method, and the follo

Python built-in dictionary dict, also known as map in other languages. Stored using the key-value method.Here is a small example of a dict:d={' Bob ': The ' Mary ': 94}print d[' Bob 'This allows you to print output 74 on the console.Here's a look at why Dict objects are inserted into corresponding key-value pairsd[' sum '] = 100print d[' Sum ']Because a key-value

I saved some username, password, host, port, and other things related to database connection as a string in the database. I want to use MySQLdb to check the connection information of these databases, you need to pass the username, password, host, port, and other information in the database information to MySQLdb as parameters. connect (). In this case, '{"host": "192.168.11.22 Prime;," port ": 3306," user ":" abc "," passwd ":" 123

; variable name [key name]ValueAdd toDictionaries are added in different ways: Dictionary variable name [newly added key name] = value corresponding to new keyModifyDictionary modification format: dictionary variable name [to modify the value corresponding to the key name] = new valueDeleteThere are three common ways to delete a dictionary, and the function is different. The following is a brief introduction to the format of these methods, the specific role and skills of the method in-depth stud

In today code a Python multithreaded code, because the need for multiple threads to share the same dict, encountered a confusion, is dict is thread safe, go to the inside check, found Daniel in the discussion, so the record, specifically also need me to further verify: In Twisted's code, DICT and list are used as th

Python exercise questions: multi-level menu (dict exercises), pythondict Menu = {'beijing': {'haidian ': {'wudaokou': {'soho ':{}, 'netease' :{}, 'Google ':{}}, 'zhongguancun ': {'iqiyi' :{}, 'car home' :{}, 'youku ':{},}, 'upgrade': {'Baidu ': {},}}, 'changping ': {'shahe': {'beihang ':{},}, 'tiantongyuan' :{}, 'huilongguan ': {},}, 'chaoyang ':{}, 'dongcheng' :{},}, 'shanghai': {'minhang ': {"People's Squ

In Python,Dictionaries are containers, so you can use the Len () method to count the number of key-value pairs in a dictionary;The dictionary is iterative, and the iteration is based on the keys in the dictionary.In, the NOT operator determines whether the specified key is in the dictionary;If you index a key that does not exist in a dictionary, an exception keyerror will be thrown;Del D[k] will delete K corresponding key-value pairs, if no k exists i

)#{' User3 ': ' Wangermazi ', ' user4 ': ' Xiaotaoqi '}My_dict.popitem ()Print(my_dict)#{' user2 ': ' Lisi ', ' user3 ': ' Wangermazi ', ' user1 ': ' Zhangsan '} City= { '1':{ 'Beijing':{ 'Chaoyang':"Xizhimen", 'Haidian':'Xibeiwang', 'Tongzhou':'Shuxi' } }, '2':"Shanghai", '3':"Liaoning"}Print(city['1']['Beijing']['Haidian'])#XibeiwangPrint(City.keys ())#Dict_keys ([' 1 ', ' 2 ', ' 3 '])Print(City.values ())#dict_values ([{' Beijing ': {

Today, the Python dictionary has been specifically tested for performance results in comparison with various methods.The test code is as follows:1 defdict_traverse ():2 fromTimeImportClock3My_dict = {'name':'Jim',' Age':' -','Height':'180cm','Weight':'60kg'}4 5T_start =clock ()6 forKeyinchMy_dict:#worst-performing notation. No optimization7 Print 'Type01.01:%s---%s'%(Key, My_dict[key])8T1 =clock ()9 Ten forKeyinchMy_dict:#The pe

Student = [{"No": 1,"score": 90},{"No": 2,"score": 90},{"No": 3,"score": 88},{"No": 4,"score": 92}]#single-level sorting, sorted by score onlystudent_sort_1= sorted (student, key=LambdaE:e.__getitem__('score'))#multilevel sorting, first according to score, and then by no sortstudent_sort_2= sorted (student, key=LambdaE: (E.__getitem__('score'), E.__getitem__('No')))Python list Nesting dict single-level sort