dict comprehension python 3

' > >> dict.setdefault (' age ', ' a ') 18>>> dict{' Color ': ' White ', ' name ': ' Tom ', ' age ': ' Hair ': ' Black '}Pretty PrintIf you import the Pprint module in a program, you can use the Pprint () and Pformat () functions, which will print beautifully a dictionary of words.The Pprint.pprint () function is especially useful if the dictionary itself contains nested lists or dictionaries.If you want nicely printed text to be a string instead of

reduce the amount of code in the function.2) Too many captures: Avoid null limit t statementsIf an empty limit t statement is used, it may intercept the events expected by the try processor at a higher level in the exception nested structure. This type of code may capture unrelated system exceptions. If a memory error occursProgram errors, iteration stops, and system releases all cause exceptions in Python. Exceptions here should not be intercepted.

) 12 >>> 13 be especially careful when operating on this type. The key of dict does not need to be of a variable type, and the key of a function does not need to be of a variable type when passing parameters. 14 eg: 15 >>> def dis (arg = []): 16... arg. append ('1') 17... print arg18... 19 >>> dis () 20 ['1'] 21 >>> dis () 22 ['1', '1'] 23 >>>> id (dis ()) 24 ['1', '1', '1'] 25 50524661526 >>> id (dis () 27 ['1', '1', '1', '1 ', '1'] 28 505246615 Refe

if the variable is a dictionary.Dictionary built-in methods: Serial Number Functions and descriptions 1 Radiansdict.clear ()Delete all elements in a dictionary 2 Radiansdict.copy ()Returns a shallow copy of a dictionary 3 Radiansdict.fromkeys ()Create a new dictionary with the keys to the dictionary in sequence seq, Val is the initial value corresponding to all keys in the di

DataThe data structure is basically---that they can handle the structure of the data or that they are used to store a set of related data.There are three types of built-in data structures in Python----- lists, tuples, and dictionariesListing (list)List is like we want to go to the supermarket to buy things list, the need to buy things listed after the whole structure is the list of data, once created we can arbitrarily add delete modify operations so

list dict str Although it is iterable iterator the list,dict,str and other iterable into Iterator You can use the iter () function:Example:iter ([]) iterator Python iterator object represents a data flow, Iterator next () function calls and returns the next data continuously until no data is thrown stopiteration error. You can think of t

'>>> Nums[' 0 ', ' 1.5 ', ' 2 ', ' 3 ']1.7 element types can be inconsistent, and can be nested>>> p = [' 1 ', ' 2 ']>>> s = [' A ', ' B ', p, ' C ']2.tuple CollectionThe tuple and list are very similar, but the tuple cannot be modified once it is initialized .The format is as follows:tuple-name= (Element1,element2,...)A variable tuple:>>> t = (' A ', ' B ', [' A ', ' B '])>>> t[2][0] = ' X '>>> t[2][1] = ' Y '>>> T(' A ', ' B ', [' X ', ' Y '])The l

. Dict Full name dictionary, using key-value (Key-value) storage, with extremely fast lookup speed.>>> d = {'Michael'Bob'Tracy ': >>>d['Michael']95Dict is a hash algorithm that calculates the storage location of value by key, so the value of key is constant. Feature is 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.

approximately the same, but returns an iterator instead of a list>>> d = {' Titile ': ' I am a tiger ', ' age ': Ten}>>> d.items (' age ', ten), (' Titile ', ' I am a tiger ' )]>>> it = d.iteritems () >>> It 7.pop--Used to get the value corresponding to the key and remove the pair of key values>>> d{' age ': ten, ' titile ': ' I am a tiger '}>>> d.pop (' age ') 10>>> d{' titile ': ' I am a tiger '}#不存在键, error >>> d.pop (' name ') Traceback (most recent): File "d.pop (

, 3, ..., 99]2, the tuple is also a list, the only difference is that the tuple is immutable. Therefore, a tuple can also be used for slicing operations, but the result of the operation is still a tuple:>>> (0, 1, 2, 3, 4, 5) [: 31, 2)A string ‘xxx‘ can also be seen as a list, with each element being a character. Therefore, a string can also be manipulated with a slice, but the result of the operation is st

As you can see from the previous sections, Python is the most basic type of programming language. List Tuple Set Dict It can be seen that the granularity of segmentation in data structure is to satisfy the need of more domain programming.1 Creating a dictionaryOther methods, such as list and tuple, can also be created, see the manual. The keys of a dictionary are non-repeatable and

, differential setIn [the]: S1 = {1,2,3}in []: s2 = {2,3,4}in []: s1.intersection (S2) out[59]: {2, 3}in []: S1 s2out[60]: {2, 3}in[A]: in [s1.union]: S2 out[61]: {1, 2, 3, 4}in [+]: S1 | S2OUT[62]: {1, 2, 3, 4}in [+]: in []: s1.difference (S2) out[63]: {1}in [+]: s1-s2out[64]: {1}in [+]: in []: S1.sym Metric_differen

/value pairs are separated by colons, and each pair is separated by commas, all of which are included in curly braces. Remember that the key/value pairs in the dictionary are not in order. If you want a specific order, then you should sort them yourself before using them. A dictionary is an instance/object of the Dict class.Example: #!/usr/bin/env python #coding: UTF8 contacts = {' Admin ': ' admin@jb

are separated by colons, and each pair is separated by commas, all of which are included in curly braces. Remember that the key/value pairs in the dictionary are not sequential. If you want a particular order, then you should sort them yourself before using them. A dictionary is an instance/object of the Dict class.Cases: #!/usr/bin/env Python#coding:utf8 contacts = {' Admin ': ' admin@jb51.net ', ' linuxe

will speak laterDict () creates dictionaries that can actually be used to generate very complex dictionaries, such as a list to constructA = Dict () # Create an empty dictionary print (type (a), a)Dir () See how the object isA = {}print (dir (a)) B = "123" Print (dir (b)) c = 123print (dir (c))Different data types, the method that can be used is not. Two __ underline is the internal method, generally can not be used, but also can be used, such as the

(temp)# Li.append (c)# result = "". Join (LI)# Print (Result)#生成字母数字, randomly generated number of digits without limit# import Random# li = []# for I in range (6):# r = Random.randrange (0,5)# if R ==2 or R ==4:# num = Random.randrange (0,10)# li.append (num)# Else:# temp = Random.randrange (65,91)# c = chr (temp)# Li.append (c)## result = "". Join (LI)# Print (Result)# compile () Compile code# python s1.py# 1, read file contents, str to memory# 2,

is_odd (x): return x%2 = = 1print(is_odd (5 ) )Print(filter (IS_ODD,A))Operation Result:true[1, 3, 5, 7]Note:1, the elements of the list are passed into the function is_odd2, is_odd to determine whether each element meets the conditions, the conditions of the left, not meet the conditions of abandonment3. Make a new list of all the elements that are ultimately eligibleEach time the function passes in an element that iterates over an object, and i

method, is as follows:"""Class Visit (list):def accept (Self,visitor):Visitor.visit_list (self)Class Vdict (Dict):def accept (Self,visitor):Visitor.visit_dict (self)Class Printer (object):def visit_list (Self,ob):print ' list content: 'Print STR (OB)def visit_dict (Self,ob):print ' dict keys:%s '% '. Join (Ob.keys ())A_list=visit ([1,2,5])A_list.accept (Printer ())A_dict=vdict ({' One ': 1, ' both ': 2, '

This chapter focuses on three very important data types in Python: List tuple dictionary#-*-Coding:utf-8-*-#1 declarations ListList1 = ["A", "B", "C"]#判断列表中是否存在元素Print ("A" in List1)#追加元素List1.append (123)#迭代输出For I in List1:Print (i)#list长度Print (len (list1))#list中最大的值max最小值minPrint (max ([12,2,3]))#pop--Removes the last value and returns the valuenumbers = [12,32,54,787,24]Print Numbers.pop ()#常用方法: Reverse Sort Remove Insert Count index#2 declaring

, post are objects of type querydict Unlike a Python dictionary, an object of type querydict is used to handle a condition with multiple values for the same key Method Get (): Gets the value based on the key Only one value of the key can be obtained If a key has more than one value at a time, get the last value dict.get(‘键‘,default)或简写为dict[‘键‘] Method GetList ()