Regular expressions

pypix advanced REGEX tips

And here's a nice cheat-sheet curtesy of HN's comments REGEX cheat sheet

Even better is [pypix advanced REGEX tips

And here's a nice cheat-sheet curtesy of HN's comments REGEX cheat sheet

Even better is](http://www.regex101.com " regular expressions 101 — an online regex tester for javascript, php, pcre and python. ") – this web-app is nothing short of amazing! You can type in all sorts of regular expression flavours and can live see how the search (and replace!) will work. More over it will interpret your regular expression into human readable instructions and give you a reason for why each matched string matched.