Learn Regex The Hard Way

The point is not to have the best or most efficient regex expression, but rather to do the exercises and to highlight by this process misconceptions you may have about how the regex engine operates.

You enter what is given, you run it, see what the console returns, ponder about the implications for a few minutes and then scream "aha!"

What do you expect ^[0-9]+|[A-Z]+$ to return when matched against the various lines? What does it actually return? What conclusions do you draw from that little experiment?

unfortunately this is not an efficiency optimization. the intent appears to be to match EITHER all-alpha OR all-numeric strings.

the regex, as given, would match both "&()ABC" and "5673%$^#" and "123ABC" but NOT "ABC123"

what should be a simple concept is defeated and confusion ensues. the correct formulation should have been ^[0-9]+$|^[A-Z]+$ or (judging from the example input and output samples) [0-9]+|[A-Z]+

I'm about 75% through his Python book, and I have to say I like it. He assumes you're an absolute beginner, and I'm not, so I can't really give it a fair appraisal from the perspective of its target audience.

That said, the book definitely makes learning fun. For the first half of the book, you have a really quick learn-reward cycle. The exercises are short and to the point, and he makes you type in the lesson and run it. This means that you type a few lines, then immediately get to see what it did, on your computer. It very much reminds me of when I was in grade 10 and we were doing simple stuff in QBasic. It would definitely grab and keep the interest of an absolute beginner dipping his or her toes into the programming pool for the first time.

From the perspective of an experienced programmer - a term I apply to myself with some trepidation - things move a bit slow, but the experienced programmer is definitely not Zed's target with the book. Even being on the slow side, the exercises are quick enough that you can knock out a bunch of lessons quickly if you're so inclined, and I've definitely skipped over a bunch of the "Extra Credit" stuff because of that.

I actually did spend the "recommended" week doing Exercise 37, which is sort of a "learn at your own pace" exercise. You're given a list of operators, string formats, keywords, etc. and asked to spend some time looking into them, defining them for yourself, and playing with them. I spent a good amount of time reading into the way Python's floor/integer division and modulo operations work / differ from other languages and why (if you're interested, Python floors towards negative infinity, not zero, and performing a modulo on negative numbers takes the sign of the divisor, not the dividend, in contrast to some other languages), and spent time toying around with decorators and lambdas.. I kept a spreadsheet of everything I was supposed to learn and my description of it. My interpretation of that lesson is probably a lot different from a beginners, but I think it's a nice example of "you get out of it what you put in."

Zed also likes to shove you into the deep end and let you learn to swim. The extra credit assignments don't have answers, they're all about making you play around and learn on your own terms. The lesson above is a good example of "here's a bunch of terms, now go play on your own for a while", which was an interesting change of pace. Also, he gives a solid emphasis on reading other peoples code. There have been at least two lessons so far dealing with that, and I've read over a bunch of reddits code and learned a good amount from that - this was during the first "go find some code" exercise, where you only know the bare minimum of conditionals and looping, so there were a lot more scary "i don't know what that code is doing, but I'm going to find out!" moments, which I found helpful.

Speaking as someone who isn't a programmer at all and needed (still needs, actually) to learn a language for dealing with a massive amount of data for a school project, I decided to have a stab at Python and have been working my way through his book. Overall I'd say it's pretty great. The good is that, as you mentioned, the early chapters (really the whole first half) are quick, repetitive exercises which I feel gave me a good understanding of the dirt basics of how Python works. Now I'm getting into the more tricky chapters and still really enjoying them.

I sometimes feel a bit more explanation from him on how or why certain things work would be nice, or maybe a few hints for where to start looking for answers in the extra credit would be good, but for the most part I think he's effectively covered enough of the basics needed to land me on the ground running. Between the exercises I've done so far and the basic script someone at reddit was kind enough to throw together for me I've managed to modify and make my own scripts to start processing the data for this project. Also it feels pretty awesome to write a script for an hour then actually see it work in less than a second and do what would have taken me days otherwise to do.

The (? ... ) syntax is for "extended patterns". In this case, it makes the rest of the regular expression case insensitive. Read through http://perldoc.perl.org/perlre.html#Extended-Patterns for more information on extended patterns.