Python Native Datatypes -- list

cdchenli

>>>  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

>>> 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

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：

['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。

>>> 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、

>>> 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：

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：

['a']
['a', 'b']
['a', 'b', 'a', 'b']
['a', 'b', 'a', 'b', 'a', 'b', 'a', 'b']