lookaround | 易学教程

Look behinds: all the rage in regex?

阅读更多关于 Look behinds: all the rage in regex?

问题 Many regex questions lately have some kind of look-around element in the query that appears to me is not necessary to the success of the match. Is there some teaching resource that is promoting them? I am trying to figure out what kinds of cases you would be better off using a positive look ahead/behind. The main application I can see is when trying to not match an element. But, for example, this query from a recent question has a simple solution to capturing the .* , but why would you use a

Alternatives to variable-width lookbehind in Python regex

阅读更多关于 Alternatives to variable-width lookbehind in Python regex

来源： https://stackoverflow.com/questions/31564195/alternatives-to-variable-width-lookbehind-in-python-regex

Does lookaround affect which languages can be matched by regular expressions?

阅读更多关于 Does lookaround affect which languages can be matched by regular expressions?

问题 There are some features in modern regex engines which allow you to match languages that couldn't be matched without that feature. For example the following regex using back references matches the language of all strings that consist of a word that repeats itself: (.+)\1 . This language is not regular and can't be matched by a regex that does not use back references. Does lookaround also affect which languages can be matched by a regular expression? I.e. are there any languages that can be

String Range forward and backward lookaround

阅读更多关于 String Range forward and backward lookaround

I am trying to write a script that gets input from a user and returns the input in a formatted area. I have been using the string range function however it obviously cuts the the input at the range that I give. Is there any way to do a look around at the specified range to find the next space character and cut the input at that location? For example, if I have the input of: Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris My current string range

RegEx - Exclude Matched Patterns

阅读更多关于 RegEx - Exclude Matched Patterns

I have the below patterns to be excluded. make it cheaper make it cheapere makeitcheaper.com.au makeitcheaper making it cheaper www.make it cheaper ww.make it cheaper.com I've created a regex to match any of these. However, I want to get everything else other than these. I am not sure how to inverse this regex I've created. mak(e|ing) ?it ?cheaper Above pattern matches all the strings listed. Now I want it to match everything else. How do I do it? From the search, it seems I need something like negative lookahead / look back. But, I don't really get it. Can some one point me in the right

RegEx - Exclude Matched Patterns

阅读更多关于 RegEx - Exclude Matched Patterns

问题 I have the below patterns to be excluded. make it cheaper make it cheapere makeitcheaper.com.au makeitcheaper making it cheaper www.make it cheaper ww.make it cheaper.com I've created a regex to match any of these. However, I want to get everything else other than these. I am not sure how to inverse this regex I've created. mak(e|ing) ?it ?cheaper Above pattern matches all the strings listed. Now I want it to match everything else. How do I do it? From the search, it seems I need something

How does this regex replacement reverse a string?

阅读更多关于 How does this regex replacement reverse a string?

问题 This is the fourth part in a series of educational regex articles. It show how the combination of nested reference (see: How does this regex find triangular numbers?) to "count" within assertions (see: How can we match a^n b^n with Java regex?) can be used to reverse a string. The programmatically generated pattern uses meta-pattern abstractions (see: How does this Java regex detect palindromes?). For the first time in the series, these techniques are used for replacement instead of whole

Need to split a string into two parts in java

阅读更多关于 Need to split a string into two parts in java

问题 I have a string which contains a contiguous chunk of digits and then a contiguous chunk of characters. I need to split them into two parts (one integer part, and one string). I tried using String.split("\\D", 1) , but it is eating up first character. I checked all the String API and didn't find a suitable method. Is there any method for doing this thing? 回答1: Use lookarounds: str.split("(?<=\\d)(?=\\D)") String[] parts = "123XYZ".split("(?<=\\d)(?=\\D)"); System.out.println(parts[0] + "-" +

How does this Java regex detect palindromes?

阅读更多关于 How does this Java regex detect palindromes?

This is the third part in a series of educational regex articles. It follows How does this regex find triangular numbers? (where nested references is first introduced) and How can we match a^n b^n with Java regex? (where the lookahead "counting" mechanism is further elaborated upon). This part introduces a specific form of nested assertion, which when combined with nested references allows Java regex to match what most people believe is "impossible": palindromes!! The language of palindromes is non- regular ; it's actually context-free (for a given alphabet). That said, modern regex

Does lookaround affect which languages can be matched by regular expressions?

阅读更多关于 Does lookaround affect which languages can be matched by regular expressions?

There are some features in modern regex engines which allow you to match languages that couldn't be matched without that feature. For example the following regex using back references matches the language of all strings that consist of a word that repeats itself: (.+)\1 . This language is not regular and can't be matched by a regex that does not use back references. Does lookaround also affect which languages can be matched by a regular expression? I.e. are there any languages that can be matched using lookaround that couldn't be matched otherwise? If so, is this true for all flavors of