Python字符串 find() 方法

如果在给定字符串中找到子字符串，则Python String find() 方法返回子字符串的最低索引。如果未找到，则返回 -1。

Syntax:

str.find(sub, start, end)

Parameters: 

• sub: It’s the substring that needs to be searched in the given string. 
• start: Starting position where the sub needs to be checked within the string. 
• end: Ending position where suffix needs to be checked within the string. 

Note #1: If start and end indexes are not provided then by default it takes 0 and length-1 as starting and ending indexes where ending indexes are not included in our search. 

Returns: 

Returns the lowest index of the substring if it is found in a given string. If it’s not found then it returns -1.

Note #2: The find() method is similar to index(). The only difference is find() returns -1 if the searched string is not found and index() throws an exception in this case.

示例 1：没有开始和结束参数的 find()

Python3

word = 'geeks for geeks'
  
# returns first occurrence of Substring
result = word.find('geeks')
print ("Substring 'geeks' found at index:", result )
  
result = word.find('for')
print ("Substring 'for ' found at index:", result )
  
# How to use find()
if (word.find('pawan') != -1):
    print ("Contains given substring ")
else:
    print ("Doesn't contains given substring")

输出：

Substring 'geeks' found at index: 0
Substring 'for ' found at index: 6
Doesn't contains given substring

示例 2：带有 start 和 end 参数的 find()

Python3

word = 'geeks for geeks'
  
# Substring is searched in 'eks for geeks' 
print(word.find('ge', 2)) 
  
# Substring is searched in 'eks for geeks' 
print(word.find('geeks ', 2)) 
  
# Substring is searched in 's for g' 
print(word.find('g', 4, 10)) 
  
# Substring is searched in 's for g' 
print(word.find('for ', 4, 11))

输出：  

10
-1
-1
6