Python Tutorial- Index Function

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How to detect if a Python string contains a substring?

Similar to the find () method, the index () method can also be used to retrieve whether the specified string is included. The difference is that when the specified string does not exist, the index() method will throw an exception.

The syntax of the index() method is as follows:


The meaning of each parameter in this format is:

  • str: the original string;
  • sub: the substring to be retrieved;
  • start: indicates the starting position of the search. If not specified, the search starts from the beginning by default;
  • end: indicates the end position of the search. If not specified, the search will continue until the end by default.

[Example] Use index () method to retrieve the index of the first occurrence of "e" in "".

string = ""

The output is:


[Example] When the retrieval fails, index() will throw an exception.

string = ""

The output is:

ValueError       Traceback (most recent call last)
[ipython-input-1-150698d84fad] in [module]
1 string = ""
----> 2 string.index('b')
ValueError: substring not found

Like find() and rfind(), string variables also have rindex() methods, which are similar to index() methods, except that they are retrieved from the right, for example:

string = ""

The output is:



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