Python中字符串如何查找？
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标签：
字符串
Python
老师回答
find方法
find方法获取值时，如果要查找的值不存在，会返回-1
str.find(str, beg=0, end=len(string))
使用实例
# string in which we have to find the sub_string
str = "Hello world, how are you?"
# sub_string to find the given string
sub_str = "how"
# find by sub_str
print (str.find (sub_str))
# find by sub_str with slice:start index
print (str.find (sub_str, 10))
# find by sub_str with slice:start index and slice: end index
print (str.find (sub_str, 10, 24))
# find a sub_str that does not exist
sub_str = "friend"
# find by sub_str
print (str.find (sub_str))
# find a sub_str with different case
sub_str = "HOW"
# find by sub_str
print (str.find (sub_str))
输出
13
13
13
-1
-1
index方法
在获取值得索引时，如果不存在值，会报错
str.index(str, beg=0, end=len(string))
使用实例
def second_index(text: str, symbol: str):
"""
returns the second index of symbol in a given text
"""
try:
return text.index(symbol, text.index(symbol) + 1)
except ValueError:
return None
if __name__ == '__main__':
#These "asserts" using only for self-checking and not necessary for auto-testing
print('Example:')
print(second_index("sims", "s"))
assert second_index("sims", "s") == 3, "First"
assert second_index("find the river", "e") == 12, "Second"
assert second_index("hi", " ") is None, "Third"
assert second_index("hi mayor", " ") is None, "Fourth"
assert second_index("hi mr Mayor", " ") == 5, "Fifth"
print('You are awesome! All tests are done! Go Check it!')
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