I have a python template engine that heavily uses regexp. It uses concatenation like:
我有一个使用regexp的python模板引擎。它使用连接:
re.compile( regexp1 + "|" + regexp2 + "*|" + regexp3 + "+" )
I can modify individual substrings (regexp1, regexp2 etc).
我可以修改单独的子字符串(regexp1、regexp2等)。
Is there any small and light expression that matches nothing, which I can use inside a template where I don't want any matches? Unfortunately, sometimes '+' or '*' is appended to the regexp atom so I can't use empty string - a "nothing to repeat" error will rise.
是否有不匹配的小而轻的表达式，我可以在不需要匹配的模板中使用?不幸的是，有时'+'或'*'被附加到regexp原子上，因此我不能使用空字符串——“没什么可重复的”错误将会上升。
7 个解决方案
#1
79
This shouldn't match anything:
任何事情都不匹配。
re.compile('$^')
So if you replace regexp1, regexp2 and regexp3 with '$^' it will be impossible to find a match. Unless you are using the multi line mode.
如果你更换regexp1,regexp2和regexp3 ' $ ^ '不可能找到一个匹配。除非你使用多行模式。
After some tests I found a better solution
经过一些测试，我找到了更好的解决方案
re.compile('a^')
It is impossible to match and will fail earlier than the previous solution. You can replace a with any other character and it will always be impossible to match
它是不可能匹配的，并且会比以前的解决方案更早地失败。你可以用任何其他字符替换a，它总是不可能匹配
#2
24
(?!) should always fail to match. It is the zero-width negative look-ahead. If what is in the parentheses matches then the whole match fails. Given that it has nothing in it, it will fail the match for anything (including nothing).
(?!)总是不匹配。这是零宽度的负面展望。如果括号中的内容匹配，则整个匹配失败。考虑到它没有任何内容，它将无法匹配任何内容(包括任何内容)。
#3
15
To match an empty string - even in multiline mode - you can use \A\Z, so:
为了匹配一个空字符串，即使是在多行模式中，你也可以使用\ \Z，所以:
re.compile('\A\Z|\A\Z*|\A\Z+')
The difference is that \A and \Z are start and end of string, whilst ^ and $ these can match start/end of lines, so $^|$^*|$^+ could potentially match a string containing newlines (if the flag is enabled).
所不同的是,A和\ \ Z是字符串的开始和结束,而^和$可以匹配的行开始/结束,所以$ ^ | $ ^ * | $ ^ +可能匹配字符串包含换行(如果启用了国旗)。
And to fail to match anything (even an empty string), simply attempt to find content before the start of the string, e.g:
如果不能匹配任何内容(即使是空字符串)，只需在字符串开始之前查找内容，例如:
re.compile('.\A|.\A*|.\A+')
Since no characters can come before \A (by definition), this will always fail to match.
因为没有字符可以在\A(根据定义)之前出现，所以这总是不能匹配。
#4
3
"()"
matches nothing and nothing only.
什么都不匹配，什么都不匹配。
#5
2
Maybe '.{0}'?
也许“{ 0 }。”?
#6
1
You could use\z..
This is the absolute end of string, followed by two of anything
您可以使用\ z . .这是弦的绝对端点，后面跟着两个
If + or * is tacked on the end this still works refusing to match anything
如果+或*被钉在末尾，这仍然有效，不能匹配任何内容
#7
0
Or, use some list comprehension to remove the useless regexp entries and join to put them all together. Something like:
或者，使用一些列表理解来删除无用的regexp条目并将它们组合在一起。喜欢的东西:
re.compile('|'.join([x for x in [regexp1, regexp2, ...] if x != None]))
Be sure to add some comments next to that line of code though :-)
请确保在代码行旁边添加一些注释:-)
#1
79
This shouldn't match anything:
任何事情都不匹配。
re.compile('$^')
So if you replace regexp1, regexp2 and regexp3 with '$^' it will be impossible to find a match. Unless you are using the multi line mode.
如果你更换regexp1,regexp2和regexp3 ' $ ^ '不可能找到一个匹配。除非你使用多行模式。
After some tests I found a better solution
经过一些测试，我找到了更好的解决方案
re.compile('a^')
It is impossible to match and will fail earlier than the previous solution. You can replace a with any other character and it will always be impossible to match
它是不可能匹配的，并且会比以前的解决方案更早地失败。你可以用任何其他字符替换a，它总是不可能匹配
#2
24
(?!) should always fail to match. It is the zero-width negative look-ahead. If what is in the parentheses matches then the whole match fails. Given that it has nothing in it, it will fail the match for anything (including nothing).
(?!)总是不匹配。这是零宽度的负面展望。如果括号中的内容匹配，则整个匹配失败。考虑到它没有任何内容，它将无法匹配任何内容(包括任何内容)。
#3
15
To match an empty string - even in multiline mode - you can use \A\Z, so:
为了匹配一个空字符串，即使是在多行模式中，你也可以使用\ \Z，所以:
re.compile('\A\Z|\A\Z*|\A\Z+')
The difference is that \A and \Z are start and end of string, whilst ^ and $ these can match start/end of lines, so $^|$^*|$^+ could potentially match a string containing newlines (if the flag is enabled).
所不同的是,A和\ \ Z是字符串的开始和结束,而^和$可以匹配的行开始/结束,所以$ ^ | $ ^ * | $ ^ +可能匹配字符串包含换行(如果启用了国旗)。
And to fail to match anything (even an empty string), simply attempt to find content before the start of the string, e.g:
如果不能匹配任何内容(即使是空字符串)，只需在字符串开始之前查找内容，例如:
re.compile('.\A|.\A*|.\A+')
Since no characters can come before \A (by definition), this will always fail to match.
因为没有字符可以在\A(根据定义)之前出现，所以这总是不能匹配。
#4
3
"()"
matches nothing and nothing only.
什么都不匹配，什么都不匹配。
#5
2
Maybe '.{0}'?
也许“{ 0 }。”?
#6
1
You could use\z..
This is the absolute end of string, followed by two of anything
您可以使用\ z . .这是弦的绝对端点，后面跟着两个
If + or * is tacked on the end this still works refusing to match anything
如果+或*被钉在末尾，这仍然有效，不能匹配任何内容
#7
0
Or, use some list comprehension to remove the useless regexp entries and join to put them all together. Something like:
或者，使用一些列表理解来删除无用的regexp条目并将它们组合在一起。喜欢的东西:
re.compile('|'.join([x for x in [regexp1, regexp2, ...] if x != None]))
Be sure to add some comments next to that line of code though :-)
请确保在代码行旁边添加一些注释:-)