Python 字符串 find()

message = 'Python is a fun programming language'

# check the index of 'fun'
print(message.find('fun'))

# Output: 12

find() 语法

find() 方法的语法是

str.find(sub[, start[, end]] )

find() 参数

find() 方法最多接受三个参数

• sub - 要在 str 字符串 中搜索的子字符串。
• start 和 end（可选）- 搜索子字符串的范围 str[start:end]。

find() 返回值

find() 方法返回一个整数值

• 如果子字符串存在于字符串中，则返回子字符串第一次出现的索引。
• 如果子字符串不存在于字符串中，则返回 -1。

find() 方法的工作原理

示例 1：不带 start 和 end 参数的 find()

quote = 'Let it be, let it be, let it be'

# first occurance of 'let it'(case sensitive)
result = quote.find('let it')
print("Substring 'let it':", result)

# find returns -1 if substring not found
result = quote.find('small')
print("Substring 'small ':", result)

# How to use find()
if (quote.find('be,') != -1):
    print("Contains substring 'be,'")
else:
    print("Doesn't contain substring")

输出

Substring 'let it': 11
Substring 'small ': -1
Contains substring 'be,'

示例 2：带 start 和 end 参数的 find()

quote = 'Do small things with great love'

# Substring is searched in 'hings with great love'
print(quote.find('small things', 10))

# Substring is searched in ' small things with great love' 
print(quote.find('small things', 2))

# Substring is searched in 'hings with great lov'
print(quote.find('o small ', 10, -1))

# Substring is searched in 'll things with'
print(quote.find('things ', 6, 20))

输出

-1
3
-1
9

另请阅读

• Python 字符串 index()
• Python 字符串 count()