v26編程指南中文版數(shù)據(jù)結(jié)構(gòu)

1、.v2 6編程指南中文版 數(shù)據(jù)結(jié)構(gòu)Navigation indexmodules|next|previous|Python v2.6.5 documentation?The Python Tutorial?5.Data Structures數(shù)據(jù)構(gòu)造?This chapter describes some things you've learned about already in more detail,and adds some new things as well.本章將更加詳細(xì)的介紹一些你已經(jīng)理解的東西，另外我們還會(huì)添加一些新的東西。5.1.More on Lists List的

2、更多細(xì)節(jié)?The list data type has some more methods.Here are all of the methods of list objects：List數(shù)據(jù)類型還有其他的一些方法。如下是List的所有方法：list.appendxAdd an item to the end of the list；equivalent to alena：=x.list.extendLExtend the list by appending all the items in the given list；equivalent to alena：=L.list.inserti,

3、xInsert an item at agiven position.The first argument is the index of the element before which to insert,so a.insert0,xinserts at the front of the list,and a.insertlena,xis equivalent to a.appendx.list.removexRemove the first item from the list whose value is x.It is an error if there is no such ite

4、m.list.popiRemove the item at the given position in the list,and return it.If no index is specified,a.popremoves and returns the last item in the list.The square brackets around the iin the method signature denote that the parameter is optional,not that you should type square brackets at that positi

5、on.You will see this notation frequently in the Python Library Reference.list.indexxReturn the index in the list of the first item whose value is x.It is an error if there is no such item.list.countxReturn the number of times xappears in the list.list.sortSort the items of the list,in place.list.rev

6、erseReverse the elements of the list,in place.An example that uses most of the list methods：如下的例子用到了上述的大部分方法：a=66.25,333,333,1,1234.5print a.count333,a.count66.25,a.count'x'2 10 a.insert2,-1a.append333a66.25,333,-1,333,1,1234.5,333a.index3331 a.remove333a66.25,-1,333,1,1234.5,333a.reversea33

7、3,1234.5,1,333,-1,66.25a.sorta-1,1,66.25,333,333,1234.55.1.1.Using Lists as Stacks將list作為堆棧使用?The list methods make it very easy to use alist as astack,where the last element added is the first element retrieved"last-in,first-out".To add an item to the top of the stack,use append.To retrie

8、ve an item from the top of the stack,use popwithout an explicit index.For example：list的方法可以讓List很輕易的變成一個(gè)堆棧來使用，而堆棧的特點(diǎn)就是最后一個(gè)被添加的數(shù)字最先被返回"last-in,first-out"。在堆棧的頂部添加一個(gè)元素，使用append方法，返回堆棧頂部的元素，使用沒有顯式指定索引的pop方法：stack=3,4,5stack.append6stack.append7stack3,4,5,6,7stack.pop7 stack3,4,5,6stack.pop6 s

9、tack.pop5 stack3,45.1.2.Using Lists as Queues將List當(dāng)做隊(duì)列?It is also possible to use alist as aqueue,where the first element added is the first element retrieved"first-in,first-out"；however,lists are not efficient for this purpose.While appends and pops from the end of list are fast,doing ins

10、erts or pops from the beginning of alist is slowbecause all of the other elements have to be shifted by one.同樣也可以將List作為隊(duì)列使用，隊(duì)列的特點(diǎn)是最先添加的數(shù)據(jù)最先返回"first-in,first-out"；不過，List對(duì)此來說并不高效。將一個(gè)元素從尾部添加或者取出非?？?，但是在List的頂部添加或者取出就會(huì)變得較慢了因?yàn)槠渌脑囟紝a(chǎn)生移位。To implement aqueue,use collections.deque which was desi

11、gned to have fast appends and pops from both ends.For example：可以用collections.deque去實(shí)現(xiàn)一個(gè)隊(duì)列，它恰恰是為了快速從兩端添加或者取出數(shù)據(jù)的。比方：from collections import deque queue=deque"Eric","John","Michael"queue.append"Terry"#Terry arrives queue.append"Graham"#Graham arrives qu

12、eue.popleft#The first to arrive now leaves'Eric'queue.popleft#The second to arrive now leaves'John'queue#Remaining queue in order of arrival deque'Michael','Terry','Graham'5.1.3.Functional Programming Tools功能性編程工具?There are three built-in functions that are ve

13、ry useful when used with lists：filter,map,and reduce.有三個(gè)內(nèi)置的函數(shù)在同list一起使用的時(shí)候非常有用：filter,map,and reduce。filterfunction,sequencereturns asequence consisting of those items from the sequence for which functionitemis true.If sequence is astring or tuple,the result will be of the same type；otherwise,it is

14、always alist.For example,to compute some primes：filterfunction,sequence返回序列中functionitem測(cè)試為真的所有元素的列表。假設(shè)sequence是一個(gè)string或者tuple，會(huì)返回和它一樣的類型，否那么返回一個(gè)list。def fx：return x%2！=0 and x%3！=0.filterf,range2,255,7,11,13,17,19,23mapfunction,sequencecalls functionitemfor each of the sequence's items and ret

15、urns alist of the return values.For example,to compute some cubes：mapfunction,sequence對(duì)隊(duì)列中的每個(gè)元素調(diào)用functionitem函數(shù)，并且返回函數(shù)所有返回值的列表。比方，計(jì)算一些立方數(shù)：def cubex：return x*x*x.mapcube,range1,111,8,27,64,125,216,343,512,729,1000More than one sequence may be passed；the function must then have as many arguments as th

16、ere are sequences and is called with the corresponding item from each sequenceor None if some sequence is shorter than another.For example：可以傳入多個(gè)隊(duì)列；不過函數(shù)必須也要有和序列數(shù)or None if some sequence is shorter than another一樣的形參數(shù)，每個(gè)隊(duì)列對(duì)應(yīng)一個(gè)形參。如下：seq=range8def addx,y：return x+y.mapadd,seq,seq0,2,4,6,8,10,12,14reduce

17、function,sequencereturns asingle value constructed by calling the binary function function on the first two items of the sequence,then on the result and the next item,and so on.For example,to compute the sum of the numbers 1through 10：reducefunction,sequence返回二參數(shù)函數(shù)function在元素上的值，其中，函數(shù)首先計(jì)算前兩個(gè)元素的值，再將返

18、回值與第三個(gè)元素計(jì)算，依次計(jì)算得到最后結(jié)果。比方，如下例子計(jì)算1到10的和：def addx,y：return x+y.reduceadd,range1,1155If there's only one item in the sequence,its value is returned；if the sequence is empty,an exception is raised.假設(shè)序列中僅有一個(gè)元素，該元素的值被返回；假設(shè)序列為空，那么會(huì)拋出異常。A third argument can be passed to indicate the starting value.In thi

19、s case the starting value is returned for an empty sequence,and the function is first applied to the starting value and the first sequence item,then to the result and the next item,and so on.For example,也可以傳入第三個(gè)參數(shù)用以表示初始值。在這種情況下，假設(shè)序列為空，那么返回該值，部位空的話，那么最開場(chǎng)計(jì)算該值與第一個(gè)元素，然后他們的結(jié)果再和第二個(gè)數(shù)計(jì)算，等等。如下：def sumseq：.de

20、f addx,y：return x+y.return reduceadd,seq,0.sumrange1,1155 sum0Don't use this example's definition of sum：since summing numbers is such acommon need,a built-in function sumsequenceis already provided,and works exactly like this.不要使用例子中sum的定義：因?yàn)榍蠛秃瘮?shù)很常用，所以一個(gè)內(nèi)建的sumsequence的已經(jīng)被提供。New in version 2

21、.3.5.1.4.List Comprehensions?List comprehensions provide aconcise way to create lists without resorting to use of map,filterand/or lambda.The resulting list definition tends often to be clearer than lists built using those constructs.Each list comprehension consists of an expression followed by afor

22、 clause,then zero or more for or if clauses.The result will be alist resulting from evaluating the expression in the context of the for and if clauses which follow it.If the expression would evaluate to atuple,it must be parenthesized.List comprehension提供了一種創(chuàng)立List的簡便方式，該方式無需使用map，filter和/或者lambda。li

23、st采用這種構(gòu)造的定義通常比List的建立過程要直觀得多。每一個(gè)list comprehension由一個(gè)表達(dá)式，以及表達(dá)式后的一個(gè)for從句，然后0個(gè)或者多個(gè)for或者if從句組成。假設(shè)表達(dá)式想要表達(dá)為一個(gè)tuple，必須用括號(hào)括起來。freshfruit='banana','loganberry','passion fruit'weapon.stripfor weapon in freshfruit'banana','loganberry','passion fruit'vec=2,4,63*x

24、 for xin vec6,12,183*x for xin vec if x312,183*x for xin vec if x2x,x*2for xin vec2,4,4,16,6,36x,x*2 for xin vec#error-parens required for tuples File"stdin",line 1,in?x,x*2 for xin vecSyntaxError：invalid syntaxx,x*2for xin vec2,4,4,16,6,36vec1=2,4,6vec2=4,3,-9x*y for xin vec1 for yin vec2

25、8,6,-18,16,12,-36,24,18,-54x+y for xin vec1 for yin vec26,5,-7,8,7,-5,10,9,-3vec1i*vec2ifor iin rangelenvec18,12,-54List comprehensions are much more flexible than mapand can be applied to complex expressions and nested functions：List comprehensions比起map來說適應(yīng)性更好，而且可以應(yīng)用到復(fù)雜的表達(dá)式和內(nèi)嵌函數(shù)：strround355/113.0,i

26、for iin range1,6'3.1','3.14','3.142','3.1416','3.14159'5.1.5.Nested List Comprehensions內(nèi)嵌List Comprehensions?If you've got the stomach for it,list comprehensions can be nested.They are apowerful tool but like all powerful tools they need to be used careful

27、ly,if at all.Consider the following example of a3x3 matrix held as alist containing three lists,one list per row：假設(shè)這很對(duì)你的胃口，我想說list comprehension還可以被嵌套。這是非常強(qiáng)大的工具，不過和許多其他強(qiáng)大工具一樣，你也必須小心慎重的使用。考慮如下的例子，一個(gè)內(nèi)含3個(gè)List的list所表示的3x3的矩陣，每個(gè)子list表示一行：mat=.1,2,3,.4,5,6,.7,8,9,.Now,if you wanted to swap rows and column

28、s,you could use alist comprehension：如今，假設(shè)你想交換行和列，你可以使用list comprehension：printrowifor row in matfor iin0,1,21,4,7,2,5,8,3,6,9Special care has to be taken for the nested list comprehension：對(duì)于內(nèi)嵌的list comprehension你需要特別的留意：To avoid apprehension when nesting list comprehensions,read from right to left.為

29、了消除嵌套list comprehensions的憂慮，我們從右到左閱讀。A more verbose version of this snippet shows the flow explicitly：下面是一段關(guān)于上述代碼流程的詳細(xì)表達(dá)：for iin0,1,2：for row in mat：print rowi,printIn real world,you should prefer built-in functions to complex flow statements.The zipfunction would do agreat job for this use case：在真實(shí)

30、世界中，你應(yīng)該更多的使用內(nèi)建函數(shù)，而不是復(fù)雜的流程語句。zip函數(shù)在這種情況下起了很大的作用：zip*mat1,4,7,2,5,8,3,6,9See Unpacking Argument Lists for details on the asterisk in this line.參閱Unpacking Argument Lists來獲取更多關(guān)于本行中星號(hào)的細(xì)節(jié)。5.2.The del statement?There is away to remove an item from alist given its index instead of its value：the del stateme

31、nt.This differs from the popmethod which returns avalue.The del statement can also be used to remove slices from alist or clear the entire listwhich we did earlier by assignment of an empty list to the slice.For example：這里提供了一種給出索引而不是值對(duì)List中元素進(jìn)展刪除的方法：del語句。與返回一個(gè)值的pop方法不同。del語句也可以用于刪除List中的一個(gè)切片甚至是整個(gè)l

32、ist早些章節(jié)里面我們提到的將一個(gè)空List賦值給切片。比方：a=-1,1,66.25,333,333,1234.5del a0a1,66.25,333,333,1234.5del a2：4a1,66.25,1234.5del a：a del can also be used to delete entire variables：del亦可以用來刪除整個(gè)變量：del aReferencing the name ahereafter is an errorat least until another value is assigned to it.We'll find other use

33、s for del later.在此以后直到它被賦值為另一個(gè)值引用名字a將產(chǎn)生錯(cuò)誤。我們將在后面探究更多del的用法。5.3.Tuples and Sequences Tuples和序列?We saw that lists and strings have many common properties,such as indexing and slicing operations.They are two examples of sequence data typessee Sequence Types-str,unicode,list,tuple,buffer,xrange.Since Py

34、thon is an evolving language,other sequence data types may be added.There is also another standard sequence data type：the tuple.我們可以看到，list與string有諸多一樣的地方，比方索引和切片操作。如下有兩個(gè)序列的數(shù)據(jù)構(gòu)造參閱Sequence Types-str,unicode,list,tuple,buffer,xrange。因?yàn)镻ython是一門正在進(jìn)化的語言，其他的序列數(shù)據(jù)構(gòu)造也會(huì)被參加。一種標(biāo)準(zhǔn)的序列數(shù)據(jù)構(gòu)造是tuple。A tuple consists

35、of anumber of values separated by commas,for instance：Tuple由逗號(hào)分開的一組值組成，比方：t=12345,54321,'hello！'t012345 t12345,54321,'hello！'#Tuples may be nested：.u=t,1,2,3,4,5u12345,54321,'hello！',1,2,3,4,5As you see,on output tuples are always enclosed in parentheses,so that nested tuples

36、 are interpreted correctly；they may be input with or without surrounding parentheses,although often parentheses are necessary anywayif the tuple is part of alarger expression.如你所見，在輸出是，tuple總是被括號(hào)括起來，這樣，嵌套的tuple也可以被正確的解釋；在輸入時(shí)，可以使用或者不適用括號(hào)，不過括號(hào)一般情況下都是必須的比方tuple是一個(gè)很大的表達(dá)式中的一部分。Tuples have many uses.For e

37、xample：x,ycoordinate pairs,employee records from adatabase,etc.Tuples,like strings,are immutable：it is not possible to assign to the individual items of atupleyou can simulate much of the same effect with slicing and concatenation,though.It is also possible to create tuples which contain mutable obj

38、ects,such as lists.Tuple有多種用處。比方：x,y坐標(biāo)對(duì)，數(shù)據(jù)庫中的雇員表等等。Tuple與string一樣，也是不可以被修改的：你不可以對(duì)tuple中的單個(gè)元素進(jìn)展賦值不過你可以使用切片以及一系列相關(guān)的操作來模擬這個(gè)效果。也可以創(chuàng)立內(nèi)含可變對(duì)象的元素，比方list。A special problem is the construction of tuples containing 0or 1items：the syntax has some extra quirks to accommodate these.Empty tuples are constructed by

39、 an empty pair of parentheses；a tuple with one item is constructed by following avalue with acommait is not sufficient to enclose asingle value in parentheses.Ugly,but effective.For example：一個(gè)比較特殊的問題是在創(chuàng)立一個(gè)只有0個(gè)或者1個(gè)元素的tuple：為了符合這種創(chuàng)立，語法上會(huì)額外多出一些怪異的東西?？誸uple使用一堆空的括號(hào)來創(chuàng)立；一個(gè)元素的tuple采用元素后加一個(gè)逗號(hào)僅僅在用括號(hào)將單個(gè)元素括起來時(shí)

40、不夠的的形式進(jìn)展創(chuàng)立。雖然很丑陋，不過可以用起來了。比方：empty=singleton='hello',#-note trailing comma lenempty0 lensingleton1 singleton'hello',The statement t=12345,54321,'hello！'is an example of tuple packing：the values 12345,54321 and'hello！'are packed together in atuple.The reverse operation

41、 is also possible：語句t=12345,54321,'hello！'是一個(gè)tuple packing的例子：12345,54321和'hello！'被打包到一個(gè)tuple中。逆向的操作也支持：x,y,z=tThis is called,appropriately enough,sequence unpacking and works for any sequence on the right-hand side.Sequence unpacking requires the list of variables on the left to hav

42、e the same number of elements as the length of the sequence.Note that multiple assignment is really just acombination of tuple packing and sequence unpacking.這被稱之為sequence unpacking，右邊的序列為任意類型皆可。序列劃分需要左邊的變量數(shù)與右邊的序列大小一致。值得一提的是，多重賦值實(shí)際上是tuple打包和分塊的結(jié)合。5.4.Sets?Python also includes adata type for sets.A s

43、et is an unordered collection with no duplicate elements.Basic uses include membership testing and eliminating duplicate entries.Set objects also support mathematical operations like union,intersection,difference,and symmetric difference.Python也有一種sets的數(shù)據(jù)構(gòu)造。set是一個(gè)未排序且元素唯一的集合。最根本的應(yīng)用包括關(guān)系測(cè)試和忽略重復(fù)的入口。Set

44、對(duì)象還支持像結(jié)合、穿插、比照和對(duì)稱比照等操作。Here is abrief demonstration：以下是一個(gè)簡單的例子：basket='apple','orange','apple','pear','orange','banana'fruit=setbasket#create aset without duplicates fruit set'orange','pear','apple','banana''orange&#

45、39;in fruit#fast membership testing True'crabgrass'in fruit False#Demonstrate set operations on unique letters from two words.a=set'abracadabra'b=set'alacazam'a#unique letters in aset'a','r','b','c','d'a-b#letters in abut not in bset

46、9;r','d','b'a|b#letters in either aor bset'a','c','r','d','b','m','z','l'a&b#letters in both aand bset'a','c'ab#letters in aor bbut not both set'r','d','b','m','

47、;z','l'5.5.Dictionaries?Another useful data type built into Python is the dictionarysee Mapping Types-dict.Dictionaries are sometimes found in other languages as"associative memories"or"associative arrays".Unlike sequences,which are indexed by arange of numbers,dictio

48、naries are indexed by keys,which can be any immutable type；strings and numbers can always be keys.Tuples can be used as keys if they contain only strings,numbers,or tuples；if atuple contains any mutable object either directly or indirectly,it cannot be used as akey.You can't use lists as keys,si

49、nce lists can be modified in place using index assignments,slice assignments,or methods like appendand extend.另外一個(gè)非常有用的內(nèi)建類型是dictionary參見Mapping Types-dict。在其他語言里面，字典通常作為關(guān)聯(lián)內(nèi)存或者關(guān)聯(lián)數(shù)組出現(xiàn)。與序列被一個(gè)范圍內(nèi)的數(shù)字索引不同，字典使用keys進(jìn)展索引，key可以是任意的不可變類型；字符串和數(shù)字通常作為key。tuple也可以作為key，假設(shè)它的元素都是字符串、數(shù)字或者tuple；假設(shè)一個(gè)tuple直接或者間接的含有一個(gè)可變的

50、元素，那么不可以作為key。你不能使用list作為key，因?yàn)閘ist可以使用索引、切片或者類似append和extend的方法進(jìn)展修改。It is best to think of adictionary as an unordered set of key：value pairs,with the requirement that the keys are uniquewithin one dictionary.A pair of braces creates an empty dictionary：.Placing acomma-separated list of key：value p

51、airs within the braces adds initial key：value pairs to the dictionary；this is also the way dictionaries are written on output.最好將字典想象為一個(gè)組未排序的key：value對(duì)，而且在一個(gè)字典中，每個(gè)key值唯一。一對(duì)花括號(hào)創(chuàng)立一個(gè)空的字典：。在其中放入一組用逗號(hào)分開的key：value對(duì)將初始化字典；這種方式也是字典打印的方式。The main operations on adictionary are storing avalue with some key and

52、 extracting the value given the key.It is also possible to delete akey：value pair with del.If you store using akey that is already in use,the old value associated with that key is forgotten.It is an error to extract avalue using anon-existent key.字典中最主要的方法是將一個(gè)值以某個(gè)鍵存入或者以某個(gè)鍵取出該值。也可以使用del刪除某個(gè)key：value對(duì)

53、。假設(shè)你用一個(gè)已經(jīng)存在的鍵存儲(chǔ)某個(gè)值，該鍵之前的值將被去除。假設(shè)采用一個(gè)不存在的鍵取值將引起錯(cuò)誤。The keysmethod of adictionary object returns alist of all the keys used in the dictionary,in arbitrary orderif you want it sorted,just apply the sortmethod to the list of keys.To check whether asingle key is in the dictionary,use the in keyword.keys方法

54、以任意順序假設(shè)你想進(jìn)展排序，只需要使用sort對(duì)鍵列表進(jìn)展排序返回字典對(duì)象中所有的鍵列表。確認(rèn)某個(gè)鍵是否在字典中存在，使用in關(guān)鍵字。Here is asmall example using adictionary：如下是一個(gè)使用字典的小例子：tel='jack'：4098,'sape'：4139tel'guido'=4127 tel'sape'：4139,'guido'：4127,'jack'：4098tel'jack'4098 del tel'sape'tel&#

55、39;irv'=4127 tel'guido'：4127,'irv'：4127,'jack'：4098tel.keys'guido','irv','jack''guido'in tel TrueThe dictconstructor builds dictionaries directly from lists of key-value pairs stored as tuples.When the pairs form apattern,list comprehension

56、s can compactly specify the key-value list.dict構(gòu)造函數(shù)直接從鍵-值列表中構(gòu)件一個(gè)字典，其中鍵-值采用tuple的形式存放在列表中。當(dāng)這些來自一個(gè)形式，list comprehension可以非常緊湊的指定一個(gè)key-value列表。dict'sape',4139,'guido',4127,'jack',4098'sape'：4139,'jack'：4098,'guido'：4127dictx,x*2for xin2,4,6#use alist comp

57、rehension2：4,4：16,6：36Later in the tutorial,we will learn about Generator Expressions which are even better suited for the task of supplying key-values pairs to the dictconstructor.在本指南的后續(xù)章節(jié)中，我們講學(xué)習(xí)更好的為dict構(gòu)造函數(shù)提供key-value對(duì)的Generator Expressions。When the keys are simple strings,it is sometimes easier

58、to specify pairs using keyword arguments：當(dāng)鍵的類型為字符串時(shí)，可以更容易的指定關(guān)鍵字參數(shù)：dictsape=4139,guido=4127,jack=4098'sape'：4139,'jack'：4098,'guido'：41275.6.Looping Techniques循環(huán)?When looping through dictionaries,the key and corresponding value can be retrieved at the same time using the iteri

59、temsmethod.在對(duì)字典進(jìn)展循環(huán)訪問的時(shí)候，使用iteritems可以同時(shí)返回鍵和對(duì)應(yīng)的值。knights='gallahad'：'the pure','robin'：'the brave'for k,v in knights.iteritems：.print k,v.gallahad the pure robin the braveWhen looping through asequence,the position index and corresponding value can be retrieved at the

60、 same time using the enumeratefunction.在對(duì)序列進(jìn)展循環(huán)訪問的時(shí)候，使用enumerate函數(shù)可以同時(shí)返回位置索引以及與之對(duì)應(yīng)的值。for i,v in enumerate'tic','tac','toe'：.print i,v.0 tic 1tac 2toeTo loop over two or more sequences at the same time,the entries can be paired with the zipfunction.在對(duì)兩個(gè)或者多個(gè)序列進(jìn)展循環(huán)訪問的時(shí)候，可以使用zip進(jìn)展配對(duì)。questions='name','quest','favorite color'answers='lancelot','the holy grail','blue'for q,a i