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可以當(dāng)成數(shù)組來用，元素下標(biāo)從0開始
Example 3.7 Negative List Indices
>>>?li
['a',?'b',?'mpilgrim',?'z',?'example']
>>>?li[?1]
'example'
>>>?li[?3]
'mpilgrim' 3、list的索引可以是負(fù)數(shù)，表達(dá)式L[n]的含義為：
（1）當(dāng)0 <= n <= len(L)-1 時(shí)， 跟java、C中的數(shù)組元素索引一樣
（2）當(dāng)-len(L) <= n <= -1 時(shí), L[n] = L[len(L)+n]
（3）n不再上述范圍內(nèi)是，程序引發(fā)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] 運(yùn)行結(jié)果：
運(yùn)行結(jié)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為整數(shù)）表示一個(gè)分片操作，注意a，b可以是任意的整數(shù)，而且分片操作永遠(yuǎn)不會(huì)引發(fā)IndexError。但是a，b取不同的值時(shí)，程序行為稍有不同。
（1）當(dāng) 0 <= a < b < len(L)時(shí)，L[a:b]返回一個(gè)由L[a], L[a+1]...L[b-1]組成的list
（2）當(dāng) 0 <= b <= a < len(L)時(shí)，L[a:b]返回空的list
（3）當(dāng)a，b取值不在上述范圍時(shí)，應(yīng)用以下4條規(guī)則替換a，b的值，得到a，b新的值后再應(yīng)用上面兩條規(guī)則。
- 若 a >= len(L), 則 a = len(L)-1
- 若 -len(L) <= a < 0, 則 a = len(L) + a
- 若 a <? -len(L)， 則? a =? 0
- b的情況跟a一樣
- 當(dāng) a沒有指定時(shí)，a = 0, 當(dāng)b沒指定時(shí)，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的參數(shù)不僅僅可以是list，也可以是一個(gè)tuple, dictionary等可以iterable的數(shù)據(jù)結(jié)構(gòu)
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 運(yùn)行結(jié)果：
運(yùn)行結(jié)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 閱讀(151)
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