Python 切片(Slice) python 在实际开发中,经常遇到下面的需求:在线性表(数组)中提取若干个元素的操作,提取规则有很多,比如说提取前5个、提取后5个、提取奇数/偶数位元素等等。 在抽样检测提取样本时,经常遇到每隔100箱牛奶,取其中一瓶作为样本进行检测。 在其他语言中,实现上述操作是依靠for循环来实现。 //例 C++...
python的slice notation的特殊用法。 a = [0,1,2,3,4,5,6,7,8,9] b = a[i:j] 表示复制a[i]到a[j-1],以生成新的list对象 b = a[1:3] 那么,b的内容是 [1,2] 当i缺省时,默认为0,即 a[:3]相当于 a[0:3] 当j缺省时,默认为len(alist), 即a[1:]相当于a[1:10] 当i,j都缺...
python 中的[::-1] 这个是python的slice notation(切片符号)的特殊用法。 a = [0,1,2,3,4,5,6,7,8,9] b = a[i:j] 表示复制a[i]到a[j-1],以生成新的list对象 b = a[1:3] 那么,b的内容是 [1,2] 当i缺省时,默认为0,即 a[:3]相当于 a[0:3] 当j缺省时,默认为len(alist), ...
Optional arguments start and end are interpreted as in slice notation. (统计指定位置内的字符个数) """ return 0 1. 2. 3. 4. 5. 6. 7. 8. 9. def encode(self, encoding='utf-8', errors='strict'): # real signature unknown; restored from __doc__ (编码的意思) """ S.encode(enco...
import mmap with open('test.txt', "r+b") as f: # memory-map the file, size 0 means whole file with mmap.mmap(f.fileno(), 0) as mm: # read content via standard file methods print(mm.read()) # read content via slice notation snippe...
这个是python的slice notation的特殊用法。 b = a[i:j] 表示复制a[i]到a[j-1],以生成新的list对象 当i缺省时,默认为0,即 a[:3]相当于 a[0:3] 当j缺省时,默认为len(alist), 即a[1:]相当于a[1:10] 当i,j都缺省时,a[:]就相当于完整复制一份a了 ...
In this tutorial, we will review the Python slice notation, and you will learn how to effectively use it. Slicing is used to retrieve a subset of values. The basic slicing technique is to define the starting point, the stopping point, and the step size – also known as stride. We will...
Optional | arguments start and end are interpreted as in slice notation. | | Raises ValueError when the substring is not found. | | isalnum(...) | S.isalnum() -> bool | | Return True if all characters in S are alphanumeric | and there is at least one character in S, False otherw...
importmmapwithopen('test.txt',"r+b")asf:# memory-map the file,size0means whole filewithmmap.mmap(f.fileno(),0)asmm:# read content via standard file methodsprint(mm.read())# read content via slice notation snippet=mm[0:10]print(snippet.decode('utf-8')) ...
我决定在Python中使用0-based索引方式的一个原因,就是切片语法(slice notation)。 让我们来先看看切片的用法。可能最常见的用法,就是“取前n位元素”或“从第i位索引起,取后n位元素”(前一种用法,实际上是i==起始位的特殊用法)。如果这两种用法实现...