How to use Python's find() function to find a substring in a string

How to use Python’s find() function to find substrings in a string

In Python string processing, it is often necessary to find substrings in a string . Python provides the find() function to help us achieve this function. This article will introduce how to use Python's find() function to find substrings in a string, and give specific code examples.

The find() function is a built-in method of the Python string object, which is used to find the position of a substring in a string. The basic usage of this function is:

str.find(sub,start,end)

Among them, str is the string to be operated on, sub is the substring to be found, start is the starting position of the search (optional, default is 0), and end is The end position of the search (optional, defaults to the length of the string).

The return value of the find() function is the index of the first character of the substring in the string. If the substring cannot be found, -1 is returned.

Next, we will demonstrate how to use the find() function through several specific examples.

Example 1:

string = "Hello, World!"
sub = "World"
position = string.find(sub)
print("子串的位置是：", position)

In this code, we define a string string and then search for the substring "World" in it. Since the substring exists within the string, the return value is the starting position of the substring. The output result of the program is:

子串的位置是： 7

Example 2:

string = "Hello, World!"
sub = "Python"
position = string.find(sub)
print("子串的位置是：", position)

This time, the substring we are looking for is "Python", which does not exist in the string, so it returns - 1. The output of the program is:

子串的位置是： -1

Example 3:

string = "Hello, Hello, Hello!"
sub = "Hello"
position = string.find(sub)
while position != -1:
    print("子串的位置是：", position)
    position = string.find(sub, position + 1)

This example shows how to find all substrings in a string. We define a loop to find substrings by continuously calling the find() function. After each search is completed, we add 1 to the position value and pass it to the find() function as the start parameter, so that we can continue to search for the next substring. The output of the program is:

子串的位置是： 0
子串的位置是： 6
子串的位置是： 12

Through these examples, we can see that it is very simple to use Python's find() function to find substrings in a string. We just need to call the function and pass the corresponding parameters. Based on the returned results, we can determine whether the substring exists and its position. In actual string processing, this function is very useful and can save us time and effort in writing complex search algorithms.

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