Python index()

python 中的index()函數有助于返回列表中給定元素的索引。我們還可以通過列表提供搜索的起點和終點。

 **list.index(element, start, end)** #where the element may be string, number, list, etc 

索引()參數:

該方法采用三個參數。此方法的輸出應該是指示元素位置的整數值。

索引()返回值

如果該方法找到給定元素的多個匹配項，它將只返回第一個匹配項的索引。

| 投入 | 返回值 | | 元素 | 元素索引 | | 如果沒有元素 | ValueError exception(值錯誤異常) |

Python 中index()方法的示例

示例 1:索引()在 Python 中是如何工作的

 # alphabet list
alphabet = ['a', 'b', 'c', 'e', 'd', 'e', 'f']

# index of 'c' in alphabet
indexpos = alphabet.index('c')
print('The index of c:', indexpos)

# element 'e' is searched
# index of the first 'e' is returned
indexpos = alphabet.index('e')

print('The index of e:', indexpos) 

輸出:

 The index of c: 2
The index of e: 3 

示例 2:如果搜索到的元素不在列表中，則索引為()

 # alphabet list
alphabet = ['a', 'b', 'c', 'd', 'e', 'f']

# index of'g' is alphabet
indexpos = alphabet.index('g')
print('The index of g:', indexpos) 

輸出:

 ValueError: 'g' is not in list 

示例 3:通過給出開始和結束參數來處理索引()

 # alphabets list
alphabets = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'd']

# index of 'c' in alphabets
indexpos = alphabets.index('c')   # 2
print('The index of c:', indexpos)

# 'd' after the 4th index is searched
indexpos = alphabets.index('i', 4)   # 7
print('The index of d:', indexpos)

# 'd' between 4rd and 6th index is searched
indexpos = alphabets.index('d', 4, 6)   # Error!
print('The index of d:', indexpos) 

輸出:

 The index of c: 2
The index of d: 7
Traceback (most recent call last):
  File "*lt;string>", line 13, in 
ValueError: 'd' is not in list