切片操作首先支援下标索引,通過[ N:M :P ]操作
索引正向從0開始,逆向從-1開始
N:切片開始位置
M:切片結束位置(不包含)
P:指定切片步長,為正數表示按照指定步長正向切片,為負數反之
一、清單的切片操作
清單切片後還是清單
通過清單生成器定義一個清單:
In [2]: a = [n for n in range(10)]
In [3]: a
Out[3]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
通過切片淺拷貝對象:
In [4]: a[:]
Out[4]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
In [5]: a[::]
Out[5]: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
指定開始切片位置:
In [6]: a[1:]
Out[6]: [1, 2, 3, 4, 5, 6, 7, 8, 9]
In [7]: a[1::]
Out[7]: [1, 2, 3, 4, 5, 6, 7, 8, 9]
指定切片範圍(不包含結束):
In [8]: a[1:5]
Out[8]: [1, 2, 3, 4]
In [9]: a[2:6:]
Out[9]: [2, 3, 4, 5]
指定步長切片:
In [10]: a[0:9:3]
Out[10]: [0, 3, 6]
In [11]: a[0:9:2]
Out[11]: [0, 2, 4, 6, 8]
指定步長方向:
In [12]: a[9:0:-2]
Out[12]: [9, 7, 5, 3, 1]
In [13]: a[9:0:-3]
Out[13]: [9, 6, 3]
通過切片逆置清單:
In [15]: a[::-1]
Out[15]: [9, 8, 7, 6, 5, 4, 3, 2, 1, 0]
二、元組切片
元組切片後還是元組,用法和清單切片一樣,但是一點需要注意
In [17]: b = (n for n in range(5))
In [18]: b
Out[18]: at 0x00000206445ED780>
# 推到式通過小括号()以後就不是元組了,是生成器的另一種形式
In [19]: b = tuple(n for n in range(5))
In [20]: b
Out[20]: (0, 1, 2, 3, 4)
In [21]: b[::-1]
Out[21]: (4, 3, 2, 1, 0)
In [22]: b[0:2:]
Out[22]: (0, 1)
三、字元串切片
字元串切片之後還是字元串,用法也和清單切片一緻
In [23]: c = "hello,world"
In [24]: c[::-1]
Out[24]: 'dlrow,olleh'
In [25]: c[0:5:]
Out[25]: 'hello'