Python 查找和索引之间的差异
我是python新手,不能完全理解find和index之间的区别Python 查找和索引之间的差异,python,string,python-2.7,Python,String,Python 2.7,我是python新手,不能完全理解find和index之间的区别 >>> line 'hi, this is ABC oh my god!!' >>> line.find("o") 16 >>> line.index("o") 16 它们总是返回相同的结果。 谢谢 未找到子字符串时返回-1 >>> line = 'hi, this is ABC oh my god!!' >>> line.find('?'
>>> line
'hi, this is ABC oh my god!!'
>>> line.find("o")
16
>>> line.index("o")
16
它们总是返回相同的结果。
谢谢 未找到子字符串时返回-1
>>> line = 'hi, this is ABC oh my god!!'
>>> line.find('?')
-1
当引发值错误时
:
>>> line.index('?')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: substring not found
>>行索引('?'))
回溯(最近一次呼叫最后一次):
文件“”,第1行,在
ValueError:未找到子字符串
如果找到子字符串,这两个函数的行为方式相同 另外,“查找”仅适用于列表、元组和字符串的as索引可用的字符串
>>> somelist
['Ok', "let's", 'try', 'this', 'out']
>>> type(somelist)
<class 'list'>
>>> somelist.index("try")
2
>>> somelist.find("try")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'list' object has no attribute 'find'
>>> sometuple
('Ok', "let's", 'try', 'this', 'out')
>>> type(sometuple)
<class 'tuple'>
>>> sometuple.index("try")
2
>>> sometuple.find("try")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'tuple' object has no attribute 'find'
>>> somelist2
"Ok let's try this"
>>> type(somelist2)
<class 'str'>
>>> somelist2.index("try")
9
>>> somelist2.find("try")
9
>>> somelist2.find("t")
5
>>> somelist2.index("t")
5
>>somelist
[“好”、“让我们”、“试试”、“这个”、“出去”]
>>>类型(somelist)
>>>somelist.index(“try”)
2.
>>>somelist.find(“try”)
回溯(最近一次呼叫最后一次):
文件“”,第1行,在
AttributeError:“列表”对象没有“查找”属性
>>>某元组
(‘好’、‘让我们’、‘试试’、‘这个’、‘出去’)
>>>类型(sometuple)
>>>sometuple.index(“try”)
2.
>>>sometuple.find(“try”)
回溯(最近一次呼叫最后一次):
文件“”,第1行,在
AttributeError:“tuple”对象没有属性“find”
>>>某物清单2
“好的,让我们试试这个”
>>>类型(somelist2)
>>>somelist2.索引(“try”)
9
>>>somelist2.find(“try”)
9
>>>somelist2.find(“t”)
5.
>>>somelist2.索引(“t”)
5.
@falsetru解释了函数之间的差异,我对它们进行了性能测试
"""Performance tests of 'find' and 'index' functions.
Results:
using_index t = 0.0259 sec
using_index t = 0.0290 sec
using_index t = 0.6851 sec
using_find t = 0.0301 sec
using_find t = 0.0282 sec
using_find t = 0.6875 sec
Summary:
Both (find and index) functions have the same performance.
"""
def using_index(text: str, find: str) -> str:
"""Returns index position if found otherwise raises ValueError."""
return text.index(find)
def using_find(text: str, find: str) -> str:
"""Returns index position if found otherwise -1."""
return text.find(find)
if __name__ == "__main__":
from timeit import timeit
texts = [
"short text to search" * 10,
"long text to search" * 10000,
"long_text_with_find_at_the_end" * 10000 + " to long",
]
for f in [using_index, using_find]:
for text in texts:
t = timeit(stmt="f(text, ' ')", number=10000, globals=globals())
print(f"{f.__name__} {t = :.4f} sec")
print()
如果找到一个子字符串,两个函数的行为都是一样的?@user1603970,是的,它们是这样的。它们的参数也是相同的。@user1603970,根据我在答案中链接的
索引文档:Like find(),但在找不到子字符串时引发ValueError。正如@reep提到的,find仅适用于as index可用于列表的字符串,tuple和stringspython应该删除这两个方法之一。其中一个很好地发挥了作用。另外,我认为index
返回-1
和find
返回ValueError
更合适,以防未找到sub
。