Be Especially Careful with non‐ASCII in Python There are some really subtle issues with how Python deals with, or fails to deal with, non-ASCII in patterns and strings. Worse, these disparities vary substantially according, not just to which version of Python you are using, but also whether you have a “wide build”. In general, when … Read more
It seems that more mainstream languages actually use their own implementation of “Perl-like” regexes than actually use libpcre. Languages that fall into this class include (at the very least) Java, JavaScript, and Python. Java’s java.util.regex library uses a syntax that’s very heavily based on Perl (approx. version 5.8) regexes, including the rules for escaping, the … Read more
You could use Unicode character properties to describe the characters: /^[\p{L}-]*$/u \p{L} describes the class of Unicode letter characters.
Okay, I have refined my regular expression based on the solution you came up with (which erroneously matches strings that start with ‘test’). ^((?!foo).)*$ This regular expression will match only strings that do not contain foo. The first lookahead will deny strings beginning with ‘foo’, and the second will make sure that foo isn’t found … Read more
Even in UTF-8 mode, standard class shorthands like \w and \b are not Unicode-aware. You just have to use the Unicode shorthands, as you worked out, but you can make it a little less ugly by using lookarounds instead of alternations: /(?<!\pL)weiß(?!\pL)/u Notice also how I left the curly braces out of the Unicode class … Read more
pip install uwsgi -I Won’t recompile the uwsgi binary, it just reinstalls the python egg. You need to rebuild the uwsgi binary with the pcre libraries. sudo apt-get install libpcre3 libpcre3-dev I think the easiest way is just to uninstall uwsgi and then run the pip installer again. pip uninstall uwsgi sudo apt-get remove uwsgi … Read more
Note that \g{N} is equivalent to \1, that is, a backreference that matches the same value, not the pattern, that the corresponding capturing group matched. This syntax is a bit more flexible though, since you can define the capture groups that are relative to the current group by using – before the number (i.e. \g{-2}, … Read more
In this case, it’s just being used as a delimiter. Generally, in PHP, the first and last characters of a regular expression are “delimiters” to mark the start and ending position of a matching portion (in case you want to add modifiers at the end, like ungreedy, etc) Generally PHP works this out from the … Read more
Perhaps the best place to start is Regex Tutorial – Possessive Quantifiers: When discussing the repetition operators or quantifiers, I explained the difference between greedy and lazy repetition. Greediness and laziness determine the order in which the regex engine tries the possible permutations of the regex pattern. A greedy quantifier will first try to repeat … Read more