How to extract characters from a string in python

String interception, also called string slicing, uses square brackets [ ] to intercept strings. In Python, a single character is also used as a string.

String [start index: end index: step size]

Start index: start interception from the specified position;

End index: end interception from the specified position, but not Contains the characters at that position.

Step size: When not specified, the step size is 1;

String [start index: end index]

First we understand Next, there are two indexing methods for strings in Python, as shown below:

Positive index means indexing from front to back, starting from 0 by default; negative index means Index from back to front; the index value can also be called a subscript. Example code:

String interception follows the principle of "left-closed, right-open", also called "left-inclusive" Package right":

[Start subscript: Start subscript)

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There are two indexing methods There are two interception methods. Example code:

Because it involves execution efficiency issues, you need to flexibly use these two index methods to intercept strings according to the situation, such as : If you want to quickly get the last part of the string, using negative index is the fastest.

>>> str='0123456789'
>>> print(str[0:3])#截取第一位到第三位的字符
012
>>> print(str[:])#截取字符串的全部字符
0123456789
>>> print(str[6:])#截取第七个字符到结尾
6789
>>> print(str[:-3])#截取从头开始到倒数第三个字符之前
0123456
>>> print(str[2])#截取第三个字符
2
>>> print(str[-1])#截取倒数第一个字符
9
>>> print(str[::-1])#创造一个与原字符串顺序相反的字符串
9876543210
>>> print(str[-3:-1])#截取倒数第三位与倒数第一位之前的字符
78
>>> print(str[-3:]) #截取倒数第三位到结尾
789
>>> print(str[:-5:-3])#逆序截取
96

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