python iterate over list

retrieved (evaluated). Therefore, it is more efficient to use memory in the case of long lists. A generator object in Python was something like a lazy list. The elements is only evaluated as soon as a iterate over them. Some notes: 1. Use loops rather than list parsing when you need to just perform a loop, which

######################################################################### str# name = "Alex"# list # classes, lists# li = [1, 9, "age", ["Shi Zhenwen", ["19", 10], "Pommeron"], "Alex", True] # objects created by the list class, Li# List Class# An object of the list class################################## #灰魔法: Methods

calculated according to an algorithm, can we continue to calculate the subsequent elements in the process of the loop? This eliminates the need to create a complete list, saving a lot of space. In Python, this side loop computes the mechanism, called the generator: Generator.To create a generator, simply change [] to () in the list-generated form. for inch #

, 8, 12]]This in turn writes the same as follows:transposed = []for i in Range (4): transposed_row = [] for row in matrix: transposed_row.append (Row[i]) Transposed.append (transposed_row) Print transposed# [[1, 5, 9], [2, 6, 10], [3, 7, 11], [4, 8, 12]]There is also a python built-in function zip (), also can be implemented as above functionZip (*matrix) # [(1, 5, 9), (2, 6, 10), (3, 7, 11), (4, 8, 12)]2.del statement (The DEL stateme

This list contains Python libraries for crawling and data processing with Web pagesInternet General Urllib-Network library (STDLIB). Requests-Network library. grab– Network library (based on Pycurl). pycurl– Network Library (binding Libcurl). Urllib3–python HTTP library, secure connection pool, support file post, high a

This list contains Python libraries for crawling and data processing with Web pages.Network General Urllib-Network library (STDLIB). Requests-Network library. grab– Network library (based on Pycurl). pycurl– Network Library (binding Libcurl). Urllib3–python HTTP library, secure connection pool, support file post, high availa

every two to get the first value Task code: print [x * (x + 1) for x in range (1,100,2)] 8.2. Complex expression (Note: This section needs to edit the code before the Sublimetext, then save as a. py file, and then the terminal starts the. py file, saves the output to an HTML file, and then opens it, and you can see the effect, and it's not clear to look at the beginning of the Python introductory article, the effect chart: ） Iterations that use

List listsMethods available in the list class (total 11 types)1. The original value was last appendedLi.append ()2. Clear the listLi.clear ()3. Copy, Shallow copyLi.copy ()4. Count the number of occurrences of an elementLi.count (value)5. Expand the original list, parameters: can iterate objectsLi.extend (objects that

Exercise One:# Compare two elements in the list, find the different elements and save in list 3L1 = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"] L2 = ["Sun", "Mon", "Tue", "Tue", "Thu", "Sat"] L3 = [] #先定义一个空列表 for i in L1: #遍历L1列表中的每一个元素 If I not in L2: #如果L1中的元素不在L2中 l3.append (i) #把元素写入L3中print(L3) #输出L3中的内容Exercise two:# Use the For statement to

The list generation, which is the comprehensions, is a very simple and powerful build of Python built-in that can be used to create lists.For example, to generate a list, [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] you can use list(range(1, 11)) :>>> list (range (1, one)) [1, 2, 3, 4, 5

directly. However, with memory limitations, the list capacity is certainly limited. Also, creating a list of 1 million elements takes up a lot of storage space, and if we just need to access the first few elements, the vast majority of the space behind it is wasted.So, if the list element can be calculated according to an algorithm, can we continue to calculate

This article mainly introduced the Python list operation usage, in the example form more detailed analysis of Python list of various common functions and the use of the method, the need for friends can refer to the This example describes the Python

1. Add a new object at the end of the list1 li=[11,22,33, ' AA ', ' BB ', ' cc ']2 li.append (' DD ') 3 print (LI)2. Clear the list1 li=[11,22,33, ' AA ', ' BB ', ' cc ']2 li.clear () 3 print (LI)3. List copy1 li=[11,22,33, ' AA ', ' BB ', ' cc ']2 li_new=li.copy () 3 print (li_new)4. Count the number of occurrences of an element1 li=[11,22,33, ' AA ', ' BB ', ' cc ', ' AA ']2 li_new=li.count ("AA") 3 print (li_new)5. Expansion of the original

; min (L3)'2 'Maxmin3. Enumerate ()Iterate over the elements in the sequence and their subscripts for in Enumerate ([+]):print11 22 3Enumerate4. SumAdd the values in the list>>> L4 = [Int ('2'), int ('4')]>>> sum (L4)6sumNote: only integers and string types can be added, otherwise an error occursIv. built-in functions defAppend (self, p_object):#add an object to the