Python中字符串如何查找？

在Python使用字符串的过程中，如果遇到很多的字符串，想要查找到想要的字符串有些困难。本文主要介绍Python字符串查找的几种方法：find方法、 index方法、rfind方法、rindex方法。具体请看如下内容：

find方法

find方法获取值时，如果要查找的值不存在，会返回-1

str.find(str, beg=0, end=len(string))

使用实例

# string in which we have to find the sub_string
str = "Hello world, how are you?"
 
# sub_string to find the given string 
sub_str = "how"
 
# find by sub_str
print (str.find (sub_str))
 
# find by sub_str with slice:start index
print (str.find (sub_str, 10))
 
# find by sub_str with slice:start index and slice: end index
print (str.find (sub_str, 10, 24))
 
# find a sub_str that does not exist
sub_str = "friend"
# find by sub_str
print (str.find (sub_str))
 
# find a sub_str with different case 
sub_str = "HOW"
# find by sub_str
print (str.find (sub_str))

输出

    13
    13
    13
    -1
    -1

index方法

在获取值得索引时，如果不存在值，会报错

str.index(str, beg=0, end=len(string))

使用实例

def second_index(text: str, symbol: str):
    """
        returns the second index of symbol in a given text
    """
    try:
        return text.index(symbol, text.index(symbol) + 1)
    except ValueError:
        return None

if __name__ == '__main__':
    #These "asserts" using only for self-checking and not necessary for auto-testing
    print('Example:')
    print(second_index("sims", "s"))

    assert second_index("sims", "s") == 3, "First"
    assert second_index("find the river", "e") == 12, "Second"
    assert second_index("hi", " ") is None, "Third"
    assert second_index("hi mayor", " ") is None, "Fourth"
    assert second_index("hi mr Mayor", " ") == 5, "Fifth"
    print('You are awesome! All tests are done! Go Check it!')

注意：
find()和index()只能找到第一个索引值。如果指定字符同时存在多个，只会输出第一个指定字符的索引值。

rfind和rindex方法用法和上面一样，只是从字符串的末尾开始查找。

以上就是Python中字符串查找的方法，大家可以选择符合自己需求的方法来解决问题哦~希望能解决你的问题。