Python offers many ways to substring a string. It is often called ‘slicing’.

Python提供了许多对字符串进行子字符串化的方法。 它通常被称为“切片”。

It follows this template:

它遵循以下模板：

string[start: end: step]

Where,

哪里，

start: The starting index of the substring. The character at this index is included in the substring. If start is not included, it is assumed to equal to 0.

start ：子字符串的起始索引。 该索引处的字符包含在子字符串中。 如果不包括start ，则假定等于0。

end: The terminating index of the substring. The character at this index is NOT included in the substring. If end is not included, or if the specified value exceeds the string length, it is assumed to be equal to the length of the string by default.

end ：子字符串的终止索引。 该索引处的字符不包括在子字符串中。 如果不包括end ，或者指定的值超过字符串的长度，则默认情况下假定它等于字符串的长度。

step: Every ‘step’ character after the current character to be included. The default value is 1. If the step value is omitted, it is assumed to equal to 1.

step ：要包括的当前字符之后的每个“ step”字符。 默认值为1。如果省略步长值，则假定等于1。

模板 (Template)

string[start:end]: Get all characters from index start to end-1

string[start:end] ：获取从索引start到end-1的所有字符

string[:end]: Get all characters from the beginning of the string to end-1

string[:end] ：获取从字符串开头到end-1的所有字符

string[start:]: Get all characters from index start to the end of the string

string[start:] ：获取从索引开始到字符串结尾的所有字符

string[start:end:step]: Get all characters from start to end-1 discounting every step character

string[start:end:step] ：获取从start到end-1的所有字符，每步字符都打折

例子 (Examples)

• Get the first 5 characters of a string

  获取字符串的前5个字符

string = "freeCodeCamp"
print(string[0:5])

Output:

输出：

> freeC

Note: print(string[:5]) returns the same result as print(string[0:5])

注意： print(string[:5])返回与print(string[0:5])相同的结果

• Get a substring of length 4 from the 3rd character of the string

  从字符串的第三个字符获取长度为4的子字符串

string = "freeCodeCamp"
print(string[2:6])

Output:

输出：

> eeCo

Please note that the start or end index may be a negative number. A negative index means that you start counting from the end of the string instead of the beginning (i.e from the right to left). Index -1 represents the last character of the string, -2 represents the second to last character and so on…

请注意，开始或结束索引可能为负数。 负索引意味着您从字符串的末尾开始而不是从头开始计数(即从右到左)。 索引-1代表字符串的最后一个字符，-2代表倒数第二个字符，依此类推……

• Get the last character of the string

  获取字符串的最后一个字符

string = "freeCodeCamp"
print(string[-1])

Output:

输出：

> p

• Get the last 5 characters of a string

  获取字符串的最后5个字符

string = "freeCodeCamp"
print(string[-5:])

Output:

输出：

> eCamp

• Get a substring which contains all characters except the last 4 characters and the 1st character

  获取一个包含最后四个字符和第一个字符以外的所有字符的子字符串

string = "freeCodeCamp"
print(string[1:-4])

Output:

输出：

> reeCode

更多例子 (More examples)

str = “freeCodeCamp”print str[-5:-2] # prints ‘eCa’
print str[-1:-2] # prints ‘’ (empty string)

• Get every other character from a string

  从字符串中获取所有其他字符

string = "freeCodeCamp"
print(string[::2])

Output:

输出：

> feCdCm

翻译自: https://www.freecodecamp.org/news/how-to-substring-a-string-in-python/