Python String index()用法及代碼示例

text = 'Python is fun'

# find the index of is
result = text.index('is')
print(result)

# Output: 7

index() 語法

它的語法是：

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

參數：

index() 方法采用三個參數：

• sub- 要在字符串中搜索的子字符串str.
• start和結尾(可選)- 在其中搜索子字符串str[開始：結束]

返回：

• 如果字符串中存在子字符串，則返回字符串中找到子字符串的最低索引。
• 如果字符串中不存在子字符串，則會引發ValueError異常。

index() 方法類似於 find() method for strings 。

唯一的區別是find()方法返回-1如果未找到子字符串，而index()拋出異常。

示例 1：index() 僅帶有子字符串參數

sentence = 'Python programming is fun.'

result = sentence.index('is fun')
print("Substring 'is fun':", result)

result = sentence.index('Java')
print("Substring 'Java':", result)

輸出

Substring 'is fun': 19

Traceback (most recent call last):
  File "<string>", line 6, in 
    result = sentence.index('Java')
ValueError: substring not found

注意：Python中的索引從0並不是1.所以發生的是19並不是20.

示例 2：index() 帶有 start 和 end 參數

sentence = 'Python programming is fun.'

# Substring is searched in 'gramming is fun.'
print(sentence.index('ing', 10))

# Substring is searched in 'gramming is '
print(sentence.index('g is', 10, -4))

# Substring is searched in 'programming'
print(sentence.index('fun', 7, 18))

輸出

15
17
Traceback (most recent call last):
  File "<string>", line 10, in 
    print(quote.index('fun', 7, 18))
ValueError: substring not found