英文:
Regex for a python string that does not start or end with specific characters
问题
我需要处理输入字符串，不能在中间包含 *，但如果它以 * 开始或结束，那么它需要以 *. 开始或以 .* 结束（不能同时出现，最多允许一个 *）。
我已经完成了检查是否在中间有 * 的第一部分，但如何添加一个条件，如果它只以 * 开始或结束，而没有 .，也是无效的。
import redef invalid_syntax(str):regex_str = r'(?<![^^])\*(?![^$])'if re.search(regex_str, str):return Truereturn False
它应该如下工作：
invalid_syntax('exampleStr') == Falseinvalid_syntax('*.exampleStr') == Falseinvalid_syntax('*exampleStr') == Trueinvalid_syntax('examp*leStr') == Trueinvalid_syntax('ex*ampleStr') == Trueinvalid_syntax('exampleStr*') == Trueinvalid_syntax('*.exampleStr*') == Trueinvalid_syntax('*.exampleStr.*') == Trueinvalid_syntax('exampleStr.*') == False
英文:
I need to process input strings that cannot have * in the middle, but if it does start or end with *, it needs to start with *. or end with .* (cannot have both, max of one * allowed)
I have the first part of checking if it has * in the middle, but how do I add on that if it starts or ends with just * without the . it is also invalid.
import redef invalid_syntax(str):regex_str = '(?<!^)\*(?!$)'if re.search(regex_str, str):return Truereturn False
It should behave as follows:
invalid_syntax('exampleStr') == Falseinvalid_syntax('*.exampleStr') == Falseinvalid_syntax('*exampleStr') == Trueinvalid_syntax('examp*leStr') == Trueinvalid_syntax('ex*ampleStr') == Trueinvalid_syntax('exampleStr*') == Trueinvalid_syntax('*.exampleStr*') == Trueinvalid_syntax('*.exampleStr.*') == Trueinvalid_syntax('exampleStr.*') == False
答案1
得分: 2
如果正则表达式证明很困难，考虑使用标准字符串操作代替。这可能会导致更符合问题描述并更容易理解/维护的代码：
def test(s):""" 我需要处理的输入字符串不能包含*，但如果它以*开始或结束，则需要以*开头或以.*结尾（不能同时具有两者，最多允许一个*） """c = s.count('*')return c == 0 or c == 1 and (s.startswith('*') or s.endswith('*'))
以下是一个测试运行：
>>> for s in ['*okay', 'okay*', 'okay', 'not*okay', '*']:... print(test(s), repr(s), sep='\t')True '*okay'True 'okay*'True 'okay'False 'not*okay'True '*'
请注意，问题说明对于是否允许单个*不是100%清楚。可能应该拒绝这种情况，因为它既以开头又以结尾。要添加这个要求，只需添加 and len(s) != 1。
英文:
If regexes prove to be a struggle, consider using standard string operations instead. That may result in code that more closely corresponds to the problem statement and be easier to understand/maintain:
def test(s):""" I need to process input strings that cannot have * in themiddle, but if it does start or end with *, it needs to startwith *. or end with .* (cannot have both, max of one * allowed)"""c = s.count('*')return c == 0 or c == 1 and (s.startswith('*') or s.endswith('*'))
Here is a test run:
>>> for s in ['*okay', 'okay*', 'okay', 'not*okay', '*']:... print(test(s), repr(s), sep='\t')True '*okay'True 'okay*'True 'okay'False 'not*okay'True '*'
Note, the problem specification is not 100% clear about whether a single * is allowed. Possibly this should be rejected because it both starts with and ends with a star. To add this requirement, just add and len(s) != 1.
答案2
得分: 1
如果您想要一个正则表达式，可以尝试使用 (regex101)：
^[^*]*$|^\*\.[^*]*$|^[^*]+\.\*$
^[^*]*$- 匹配如果字符串不包含*
或者：
^\*\.[^*]*$- 匹配如果字符串以*.开始并且不包含额外的*
或者：
^[^*]+\.\*$- 匹配如果字符串以.*结尾并且不包含额外的*
英文:
If you want one regex you can try (regex101):
^[^*]*$|^\*\.[^*]*$|^[^*]+\.\*$
^[^*]*$-> match if string doesn't contain*
or:
^\*\.[^*]*$-> match if string begins with*.and doesn't contain additional*
or:
-
^[^*]+\.\*$-> match if string ends with.*and doesn't contain additional*
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