Example 3.6 Defining a List
>>>
li
=
[
"
a
"
,
"
b
"
,
"
mpilgrim
"
,
"
z
"
,
"
example
"
]
>>>
li
[
'
a
'
,
'
b
'
,
'
mpilgrim
'
,
'
z
'
,
'
example
'
]
>>>
li[0]
'
a
'
>>>
li[
4
]
'
example
'
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
>>> li
['a', 'b', 'mpilgrim', 'z', 'example']
>>> li[−1]
'example'
>>> li[−3]
'mpilgrim' 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
li = ['a', 'b', 'String', 'list', 'dictionary']
print li[0:3]
print li[:]
print li[:3]
print li[1:]
print li[0:7] # won't cause IndexError
print li[-2:-1] # identical to li[len(li)-2 : len(li)-1]=li[3:4]
print li[-1:-2] # identical to li[4:3], so it will return a empty list
print li[-125:1159] 运行结果：
运行结果
['a', 'b', 'String']
['a', 'b', 'String', 'list', 'dictionary']
['a', 'b', 'String']
['b', 'String', 'list', 'dictionary']
['a', 'b', 'String', 'list', 'dictionary']
['list']
[]
['a', 'b', 'String', 'list', 'dictionary']
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
>>> li = ['a', 'b', 'c']
>>> li.extend(['d', 'e', 'f'])
>>> li
['a', 'b', 'c', 'd', 'e', 'f']
>>> len(li)
6
>>> li[−1]
'f'
>>> li = ['a', 'b', 'c']
>>> li.append(['d', 'e', 'f'])
>>> li
['a', 'b', 'c', ['d', 'e', 'f']]
>>> len(li)
4
>>> li[−1]
['d', 'e', 'f' 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
>>> li = ['a', 'b', 'mpilgrim']
>>> li = li + ['example', 'new']
>>> li
['a', 'b', 'mpilgrim', 'example', 'new']
>>> li += ['two']
>>> li
['a', 'b', 'mpilgrim', 'example', 'new', 'two']
>>> li = [1, 2] * 3
>>> li
[1, 2, 1, 2, 1, 2] 注意下面的例子：
Another Example
li = ['a']
print li
#li = li + 'b' TypeError: can only concatenate list (not "str") to list
li += 'b'
print li
li = li * 2
print li
li *= 2
print li 运行结果：
运行结果
['a']
['a', 'b']
['a', 'b', 'a', 'b']
['a', 'b', 'a', 'b', 'a', 'b', 'a', 'b']
posted on 2007-08-27 21:11
Jeff Lee 阅读(147)
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