How to intercept a string and obtain a substring

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Release: 2019-05-25 10:56:50
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For example, if there is a string, python, how to get the first 3 digits, or the last 2 digits. Record it here.

How to intercept a string and obtain a substring

Operation process:

1. Obtain the substring in the string by using separators and subscripts

>>> text = 'python' >>> text[0-2] #使用 - 这种方式发现并没有获取想要的 'o' >>> text[0:2] #使用冒号 : 分割符,获取位置0到位置2,但是不包括位置2的字符,即 p y 0位置,1位置 'py' >>> text[3:4] #获取位置3,4,但是不包括位置4,那么只是去位置3上的字符 'h' >>> text[2:5] #获取2,3,4位置上的字符 'tho
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Remarks: Always include the starting position and always exclude characters at the end position. n:m includes the n position, but does not include the m position.

2. The default value of the subscript.

>>> text[:2] #如果冒号左边没有值,就是从0开始,即省略了第一个值,默认是0,就是0:2 'py' >>> text[2:] #2:从2开始,一直到结束,省略冒号后面的索引值,就是这个字符串的长度,python长度是6,就是2:6 'thon' >>> text[:2] + text[2:] #[:2] + [2:] 就是整个字符 'python' >>> text[-2:] #备注:这个是从倒数第2个字符到结尾。 'on' >>> text[-4:] #从倒数第4个字符到结尾 'thon'
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Note: The subscript has a default value.

3. What to do if the subscript exceeds the range when using splitting

>>> text[3:40] #如果结束的下标,超过了范围,那么自动到字符串结尾 'hon' >>> text[21:] #如果开始的下标都超过了字符串长度,那么就是返回空字符串 '' >>> text[21:2] #同样,开头的下标超过了字符串长度,结束下标就不看了,也没有报错,而是返回空字符串 ''
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