The reason why I like Python so much is the way I can solve some simple problems – solutions are simple and good looking. One of the examples I use to give when asked “what does it mean that code is good looking” is checking if word is a palindrome.
Using Hadoop may quickly become very annoying if you have to navigate through the HDFS filesystem with a standard
hadoop command. As a Linux user I got used to TAB-autocompletion feature, which lets me quickly and easily use my filesystem so I was really disappointed with this difficulty. Luckily – there’s a solution which eased my pain!
Few weeks ago I’ve bought a new laptop and I’ve installed a new Xubuntu 11.10 on it. Surprisingly (and sadly), when I tried to connect an external display to it, I found out that it’s impossible to do it in “out of the box” version of Xubuntu. I had only a choice to use my external display instead of the internal one or to do a “mirror” configuration, having the same on both displays… Satisfying? No, thanks. I had to find out how to do it in the way I want it to work.
Just a quick tip if you try to set up Hadoop on your Ubuntu 11.10 and you wonder if Maverick’s version will work – yes, it will. Just follow the installation guide inserting this:
deb http://archive.cloudera.com/debian maverick-cdh3 contrib deb-src http://archive.cloudera.com/debian maverick-cdh3 contrib
/etc/apt/sources.list.d/cloudera.list – that’s it!
OK, not exactely – some people (I was one of them) report a
NullPointer Exception. Something similar to this:
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Error: java.lang.NullPointerException at java.util.concurrent.ConcurrentHashMap. get(ConcurrentHashMap.java:768) at org.apache.hadoop.mapred.ReduceTask$ ReduceCopier$GetMapEventsThread. getMapCompletionEvents(ReduceTask.java:2683) at org.apache.hadoop.mapred. ReduceTask$ReduceCopier$GetMapEventsThread. run(ReduceTask.java:2605)
check your Hadoop host settings (preferrably use IP instead of hostname) and/or
/etc/hosts, which may contain a strange entry with something like
.(null) – just leave one, proper hostname in that line. For me – it started to work after this fix.
I won’t risk saying that it’ll be OK for production enviroment (production server with Ubuntu? OK…), but for testing – it works perfectly.
Few days ago I was talking with my friend about most useful Python features we use almost every day. It was not about any sophisticated tools or libraries, but about the things we use often and which are “given” by the language and its syntax itself – the ones which we like just because they’re “pythonic”. I’ve picked and some of them, which are easy to describe in short devblog article. Even if most of these things should be known for most of the Python developers, I bet that many of you don’t know about at least one of them or just use to forget about using it ;)
Sometimes things don’t work in the way we want them to. Today I was asked why this piece of code is not working properly (OK, given problem was a bit different and much more “real-life-applicable”, but it’s just an example):
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def mypush(val, mylist=): mylist.append(val) print mylist, ': ', id(mylist) lst =  mypush(1, lst) mypush(2, lst) mypush(1) mypush(2)
The output is:
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 : 139750946213184 [1, 2] : 139750946213184  : 139750946218496 [1, 2] : 139750946218496
What’s wrong with it? NOTHING – that’s the way Python should and will behave in such case.
Do you agree? If yes – stop reading, because you won’t learn anything new. Go to XKCD instead. If no – here’s a brief explaination:
No matter what you do, sometimes you just need to swap some values – I guess you did it thousand times. And yes, I know – this problem is trivial. In Python it’s completely trivial. You just swap two variables in the most “natural” way:
a, b = b, a
instead of doing it this way:
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tmp = a a = b b = tmp
Beautiful! This is why we love Python, isn’t it?
That’s the moment where I should end this post, if it was about doing it in a “pythonic” way only. But it’s not – it’s about the ideas, not the solutions in any specific language. So…
How, as a programmer, could I start this blog if not this way:
print "Hello World"
In Poland we call poor jokes like this “suchar”, which means something like “hardtack”.
Now it can only be better ;)