Jafe Lee

  BlogJava :: 首页 :: 新随笔 :: 联系 :: 聚合  :: 管理 ::
  49 随笔 :: 0 文章 :: 24 评论 :: 0 Trackbacks
Example 3.6 Defining a List
1、list的元素是有序的
2、list可以当成数组来用,元素下标从0开始
Example 3.7 Negative List Indices
3、list的索引可以是负数,表达式L[n]的含义为:
(1)当0 <= n <= len(L)-1 时, 跟java、C中的数组元素索引一样
(2)当-len(L) <= n <= -1 时, L[n] = L[len(L)+n]
(3)n不再上述范围内是,程序引发IndexError
Slicing a list
运行结果:
运行结果
4、L[a:b](其中a,b为整数)表示一个分片操作,注意a,b可以是任意的整数,而且分片操作永远不会引发IndexError。但是a,b取不同的值时,程序行为稍有不同。
(1)当 0 <= a < b < len(L)时,L[a:b]返回一个由L[a], L[a+1]...L[b-1]组成的list
(2)当 0 <= b <= a < len(L)时,L[a:b]返回空的list
(3)当a,b取值不在上述范围时,应用以下4条规则替换a,b的值,得到a,b新的值后再应用上面两条规则。
  • 若 a >= len(L), 则 a = len(L)-1
  • 若 -len(L) <= a < 0, 则 a = len(L) + a
  • 若 a <  -len(L), 则  a =  0
  • b的情况跟a一样
  • 当 a没有指定时,a = 0, 当b没指定时,b=len(L)-1
5、append和extend方法的不同,看下例就一目了然了。
the difference between extend and append
注意 extend的参数不仅仅可以是list,也可以是一个tuple, dictionary等可以iterable的数据结构
6、

List object methods

Method

Description

Nonmutating methods

 

L.count(x)

Returns the number of items of L that are equal to x.

L.index(x)

Returns the index of the first occurrence of an item in L that is equal to x, or raises an exception if L has no such item.

Mutating methods

 

L.append(x)

Appends item x to the end of L ; e.g., L[len(L):]=[x].

L.extend(s)

Appends all the items of iterable s to the end of L; e.g., L[len(L):]=s.

L.insert(i, x)

Inserts item x in L before the item at index i, moving following items of L (if any) "rightward" to make space (increases len(L) by one, does not replace any item, does not raise exceptions: acts just like L[i:i]=[x]).

L.remove(x)

Removes from L the first occurrence of an item in L that is equal to x, or raises an exception if L has no such item.

L.pop([i])

Returns the value of the item at index i and removes it from L; if i is omitted, removes and returns the last item; raises an exception if L is empty or i is an invalid index in L.

L.reverse( )

Reverses, in place, the items of L.

L.sort([f]) (2.3)

Sorts, in place, the items of L, comparing items pairwise via function f; if f is omitted, comparison is via the built-in function cmp. For more details, see "Sorting a list" on page 57.

L.sort(cmp=cmp, key=None, reverse=False)(2.4)

Sorts, in-place, the items of L, comparing items pairwise via the function passed as cmp (by default, the built-in function cmp). When argument key is not None, what gets compared for each item x is key(x), not x itself. For more details, see "Sorting a list" on page 57.

7、
List Operators
注意下面的例子:
Another Example
运行结果:
运行结果

posted on 2007-08-27 21:11 Jafe Lee 阅读(304) 评论(0)  编辑  收藏 所属分类: Book Notes--Dive Into Python

只有注册用户登录后才能发表评论。


网站导航: