Python中切片的詳細操作篇

>> a = [1,2,3,4,5,6]
>>> a[0] ##單個數,代表位數,第0位就是a裡面的第一位
1
>>> a[5]##a裡面的第5位,注意要從0作為第一位開始數
6

>>> b=[6,3,6,7,8,2,5,4]
>>> b[:] ##單獨一個冒號,代表從頭取到尾,步長預設為1
[6, 3, 6, 7, 8, 2, 5, 4]
>>> b[::]##單獨兩個冒號一樣代表從頭取到尾,步長預設為1
[6, 3, 6, 7, 8, 2, 5, 4]
>>> b[::-1]##注意,兩個冒號後面是步長,步長為1,故應從右往左取
[4, 5, 2, 8, 7, 6, 3, 6]

>>> a 
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 
>>> a[1:6] ##預設步長為1,從左往右,注意前閉後開
[1, 2, 3, 4, 5] 
>>> a[1:6:-1] 
[] ## 當取值的大小方向與步長的方向衝突時,返回值是空.
>>> a[6:1:-1] 
[6, 5, 4, 3, 2] 
>>> a[:6] ## 沒有star代表從頭開始取
[0, 1, 2, 3, 4, 5] 
>>> a[:6:-1] 
[9, 8, 7] 
>>> a[6:] 
[6, 7, 8, 9] 
>>> a[6::-1] 
[6, 5, 4, 3, 2, 1, 0] 

>>> a 
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 
>>> a[:-6] ## -6意思是從右往左數的第六位,故第六位是4,然後預設步長為1(從右往左),star未寫,故從頭開始取到4
[0, 1, 2, 3] 
>>> a[-1:-6] 
[]
>>> a[-1:-6:-1] 
[9, 8, 7, 6, 5] 
>>> a[-6:-1] ## 這個是從-6取到-1,步長為1,意思是從右往左數第6位到從右往左的第一位
[4, 5, 6, 7, 8] 
>>> a[:-6:-1] ## 這個是從0取到-6,步長為-1,因為開頭是冒號,故起點被隱藏了
[9, 8, 7, 6, 5] 
>>> a[-6:] 
[4, 5, 6, 7, 8, 9] 
>>> a[-6::-1] ## 注意這個不等於[-6:-1],區別是這裡是::(兩個冒號),兩個冒號後連線的是步長
[4, 3, 2, 1, 0]

>>> a 
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 
>>> a[1:-6] 
[1, 2, 3] 
>>> a[1:-6:-1] 
[]
>>> a[-1:6] 
[]
>>> a[-1:6:-1] 
[9, 8, 7] 

>>> a 
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 
>>> a[:8][2:5][-1:] ## [:8]就是0取到8,在從其中取2到5,最後取-1位
[4] 
a[:8] ---- [0,1,2,3,4,5,6,7] 
[0,1,2,3,4,5,6,7][2:5]----[2,3,4] 
[2,3,4][-1:] ----[4] 

>>> a 
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 
>>> a[1+2:2*3:7%2]  ## 思路一樣,運算出來,繼續切
[3, 4, 5] 

>>> t = (1,2,3,4,5) 
>>> t[1:3] 
(2, 3) 
>>> s = "ACDRF" ##切片在字母上也是可以使用的,所以說切片很強大
>>> s[1:3] 
'CD' 
>>> (0, 1, 2, 3, 4, 5)[:3]#元組的切片操作
>>> (0, 1, 2)
>>> for i in range(0,100): 
... print(i) 
... 
>>> for i in range(0,100)[2::3][-10:]: ## 意思是從第二位開始取,步長為3,[-10]則是從倒數10位開始取,意思是去末尾10位.
... print(i) 
... 
71
74
77
80
83
86
89
92
95
98

 >>> a
 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
 >>> a[0:6:2]
 [0, 2, 4]
 >>> a[::2]
 [0, 2, 4, 6, 8]
 >>> a[:-2:2]
 [0, 2, 4, 6]
 >>> a[4::2]
 [4, 6, 8]

 >>> a
 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
 >>> a[5::-1]
 [5, 4, 3, 2, 1, 0]
 >>> a[:4:-2]
 [9, 7, 5]
 >>> a[::-1]
 [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]