You've probably already got it, I'm surveying several sites to improve programming skills. This episode is about Codecademy.

It's a very well done site, for people that want to learn a language. It has a Python track, along with several others: Ruby, JQuery, Javascript & so on.

You'll be required to actually write code and run it! yes, the code you write is then executed in a web "interpreter" (modified for educational purposes) and the output displayed on screen. In a section is also possible to write to files and have their contents shown on another tab.

I'd encourage you to start from it if you never saw Python and you're willing to learn if from the ground up.

I've played a bit with Project Euler but all of their problems are math-centric, which is nice but not exactly what I'm looking for: some real-world programming problems to get back into the coding field.

So asking my friend Google, I found CodingBat: it has a Python section with several tasks to complete. I must say they are some kinda trivial to solve, once you know some idiomatic Python code, but some are a bit more interesting. If you're a junior Python coder, or want to get a grip on the language, give it a look.

Oh, and if you know some website that would give me some real-world programming coding problems (something that would be useful on the job, not just coding for fun), I would love to hear you.

Here's my solution to Project Euler problem 4:

# handy function to check if a number is palindrome
def is_palindrome(i):
    return str(i) == str(i)[::-1]
# what's the max?
max_p = 0
# multiply all numbers  i  between 100 and 998, with all between i+1 and 999
for i in xrange(100, 999):
    for j in xrange(i+1, 1000):
        p = i * j
        if is_palindrome(p) and p > max_p:
            max_p = p
print max_p

Comments are welcome.

Update: fixed as per Alex comment.

Here's my solution to Project Euler problem 6:

# where the numbers list ends
n = 100
# handy function to square a number
pow2 = lambda x: pow(x, 2)
# first compute the sum of the squares
sumsq = sum(map(pow2, range(1, n+1)))
# then the square of the sum
sqsum = pow2(sum(range(1, n+1)))
print sqsum - sumsq

I'm the maintainer of MySQL Connector/Python Debian package, and it's shipped with several unittests, but they require a MySQL instance to be run against, so up to know I wasn't able to run them at build-time.

But I want to change that, so I wanted to find a way to spawn a MySQL instance just for testing purposes. I've searched a lot, and then found a package solving the same problem: php5.

The package has a setup-mysql.sh script that takes care of starting/stopping the instances, and debian/rules file sets up instance parameters and then it starts the instance before the tests and then stops it after them.

It's a very interesting solution, so I thought of sharing + taking notes to self, just in case I need it in other situations.

I've been using a Google account since years, but having a "more serious" one along. The time has come to make the switch and elect the other as main one.

Google has a lot of services, and I'm using several of them, so changing the main account requires to migrate data of those services to the new account, given it's not possible to merge two accounts. To know the full list of services your account is signed in, go to your Account Product page. Some migrations are easy, others hell no: so I'm writing this post to keep track of the migration as it's going on.

First of all, there's a really good post about this migration at LifeHacker: it contains a lot of info I'm using here, but not all the services I need. Additionally, Google has a list of services and methods to migrate from one account to another.

Just to be generic, I'll call AccountSRC the original account and AccountDST the one I want to migrate to.

Migrate GMail

GMail is probably the most important service I have, and also the most difficult one to migrate. I have a lot of filters, so the first step is to migrate them:

1. Login into GMail for AccountSRC
2. Gear icon > Settings > Labs
3. Enable the "Filter import/export" plugin
4. Reload GMail to enable the plugin (if not done automatically)
5. Gear icon > Settings > Filters
6. At the bottom of the page, Select all
7. Export: this will download an XML file with the filters in it
8. Login into GMail for AccountDST
9. Enable "Filter import/export" plugin
10. Load the file containing the saved filters
11. Import all (or select which one) filters; this will also create automatically the labels defined in the filters.

I currently have a forward rule from AccountDST to AccountSRC: so let's revert the forward direction: from AccountSRC to AccountDST. This will allow the new account to receive the mails sent to the old one.

1. Login into GMail for AccountDST
2. Gear icon > Forwarding and POP/IMAP > Disable forwarding: this will stop redirecting mails from AccountDST to AccountSRC
3. Login into GMail for AccountSRC
4. Gear icon > Forwarding and POP/IMAP > add a forwarding address
5. Enter AccountDST as the address to forward mails to
6. A verification code is sent to AccountDST and you'll need to enter that code in AccountSRC to verify you have access to both mailboxes
7. Once verified, select "Forward a copy of incoming mail to" to AccountDST and to delete the GMail copy on AccountSRC

Migrate Contacts

Contacts are available inside GMail:

1. Login into GMail for AccountSRC
2. On the combobox on top-left, select Contacts
3. More > Export
4. Export all the contacts in Google CSV, since it's specific to be re-imported
5. Login into GMail for AccountDST
6. Contacts > More > Import
7. Select the previously saved file and import it

Migrate Reader

Migrating Reader subscriptions is easy:

1. Login into Reader for AccountSRC
2. Reader Settings -> Import/export
3. Export your subscriptions in OPML format
4. Now login into Reader for AccountDST
5. Reader Settings -> Import/export
6. And import the saved OPML file

Migrate Blogger

Login to Blogger for AccountSRC; then, for each blog you have there do this dance:

1. Select the blog
2. Go into Settings > Permissions
3. Add AccountDST as a new author: this will send an email to AccountDST GMail account
4. Accept the invitation (this will ask you to create a new Blogger account for AccountDST if you don't already have one)
5. Go back to to Blogger with AccountSRC
6. Blog > Settings > Permissions
7. Grand admin rights to AccountDST

In software development, you often need to know: when was this feature released? in which releases was this changeset included?

Typical example is: you're debugging a problem, you find out what's the changeset introducing it, now you want to know when that changeset was firstly released (i.e. included in a tag) - how to do that?

hg log -r "cset:: and tag()"

where cset is the changeset you're looking for.

So know I know that Sphinx new way to load searchindex.js was introduced in the this changeset, and released for the first time in 1.0b2:

$ hg log -r "423faa03c908:: and tag()"
changeset: 2261:b494009dccf1
tag: 1.0b2
user: Georg Brandl <georg@python.org>
date: Sun May 30 19:52:08 2010 +0200
summary: Release preparation for 1.0b2.
...

awesome!

PS: why did I need to know that? because Matplotlib is still using the old way, but Debian needs the new one.

I received the email yesterday and was like wow, I m in . I would like to thank:

• Raphael Hertzog and Roland Mas who motivated me to contribute to the Debian project in the first place.
• Sandro Tosi, who taught me a lot while I have been working on Reportbug.
• A huge, huge thanks to Piotr O arowski, who patiently sponsored all the packages I asked him to review.
• Xavier Oswald who allowed me to start the NM process.
• And finally a huge thanks to Martin Zobel-Helas and Holger Levsen who were my application managers.

Sorry for the other readers who will find this post boring, but it means a lot to me

uniq is a great tool, since it returns the unique (adjacent) lines of the given input. But it has a limitation: it can't check for uniqueness only the first N fields (while it allows to ignore them, weird).

So, what to do if you have a long file, and lines with several fields, but you're only interested in getting the line with the different first 2 field (but all the rest of the line content? awk to the rescue!

$ awk '!x[$1]++' file

will print the (complete) lines of file that has the first field unique. You can set $1$2 to have lines unique on the first 2 fields, and so on. Thanks to this forum post, but there's some other interesting articles.

I thought it would have been easier to print a NUL-terminated string in awk (mawk as it's the default in Debian), but after some trial-and-fail I was able to come up with this kinda ugly solution:


$ echo -e "123\n456" awk 'BEGIN ORS="" print $0 ; printf("%c", "") ' xargs -n1 -0 echo
123
456

That:

• set the Output Records Separator (ORS) to the empty string (default is the \n, new line)
• print the input line (do your elaboration there, if you need)
• print the null character, as explained in the mawk manpage: "mawk cannot handle ascii NUL \0 in the source or data files. You can output NUL using printf with %c, and any other 8 bit character is acceptable input."
• show that it's actually emitting NUL-terminated strings

What to get the files older than today? Run

find /path/ -type f -daystart -mtime +0

it will return only the files older than today, no matter the time the command is executed (by default, -mtime counts multiples of 24 hours from now). Kinda nice when you want to archive yesterday log files.

I like so much the git feature branch workflow, that in the early days of development on Python with Mercurial I created some named branches; well, that is something you should not do.

In Mercurial, the changeset contains the branch name, so you cannot develop on a separated (named) branch and then merge on default and hope that branch goes away, because it will stay.

What do I do now? Python Mercurial repository is quite big (around 200Megs) so I wanted to avoid to re-check it out. Thanks to the help of the folks on #mercurial (on freenode IRC network) I found my solution: strip the branch!

Please note that strip is dangerous. Use it only as last resort, and mind you can lose data with it. That said, it's a very powerful tool :) My main aim was to remove completely those named branches, leave no traces, and lose the changes I made on them. Another important aspect is that I didn't merged those branches on default.

So, how to get rid of a named branch:

$ hg strip "branch($ BRANCHNAME )"

and re-iterate for all the branches you have, that's it. Now, to be completely sure they were removed and no spurious changes are in the repository, you can:

$ hg pull -u
$ hg outgoing

and if it says "no changes found" you're sure that those branches are really gone.

Yeah, since a couple of hours I'm officially a Python Core Developer (and this confirms it, so I'm not dreaming!)

I'm now in that mixed state in between the happiness and the fear I'll do stupid mistakes and I'll be ashamed of myself. But hey, it's only those who do nothing that make no mistakes.

Interesting days ahead, a lot of procedures to learn and get used to, hopefully also a lot of bugs fixed :) That's for sure, I'll go step by step, following the better be safe than sorry rule.

At the end, I'd like to thank all the people at Python that made this possible, they are quite a number, so if I'd named them, I surely forgot someone, and it would be unfair! So well, you know who you are, and this big THANK YOU is yours :)

Debian mailing lists' standard policy is to allow posts from unsubscribed users. That of course fits our standards for opened development but has the drawback of allowing a lot of spam to reach our mailing lists. This spam also clutters the mailing lists archives. Since 2009, a working system allows removing spam from the mailing list archives. Today, I would like to put some light on the results of this system :

• Over one million nominations for spams (a "nomination" means that someone reporting that a said post is likely to be a spam mail)
• Nearly fourty thousand individual messages considered for review
• Nearly ALL of these processed by Sandro Tosi, leader of the tireless reviewers team. Let's bend at Sandro.
• Out of these, over thirty-three thousand messages classified as spam and removed from the archives

Results are impressive for mailing lists where a coordinated effort is done over time: the debian-boot mailing list (first coorindated effort, initiated by regretted Frans Pop), the Italian and French mailing lists. You want to help? You can. Reporting spam is as easy as reading Debian mailing lists. When you see a mail that you consider being a spam mail, just bounce it to report-listspam at lists dot debian dotte org. Don't forward it, you need to bounce it ("b" keyboard shortcut in mutt). Alternatively, you can check for this message on Debian mailing lists archives and hit the "Report as spam" button. If you're a Debian developer, you can help in reviewing nominated spam. It takes me about 20 minutes every week. Go to the spam review home page and register for an account there. Then, you'll be able to process through nominated posts. Once a given post is confirmed as spam by at least 3 reviewers with nobody else reporting it as "ham", it is removed the next week from the archive. Feel free to join the game and be part of the Debian moppers team!

I procrastinated to look up this for such a long time.. today was enough. What I want to achieve is reading a line from stdin and split it among several variables, naively I'd do:

$ echo "A BB CCC" read a b c
$ echo $a $b $c


(no output.) As well explained here the above code doesn't work, but this one does:

$ read a b c < <(echo "A BB CCC")
$ echo $a $b $c
A BB CCC

as a hint, <(cmds) is called process substitution.

I just got confirmation my company will sponsor me for EuroPython 2011 (thanks Register.it), so I'll be able to attend the whole week; a lot of amazing talks and the code sprints in the weekend: this is going to be a great time!

Are you coming?

A long list, and you want to process its items n at a time; easy, but how to split that list in sublists of n elements (except the last one, of course)?

I looked a bit into the stdlib but it doesn't seem to exist anything I could use (oh, did I say I'm still on 2.4?) so I directed my research to Google, and found a nice recipe at ActiveState, but it has the problem it discards the last list, if it has less than n items.

Searching again, I got more lucky with this article: it's a generator of tuples from a list, splitting every n elements and optionally return the last semi-full tuple. I slightly modified it to obtain:

def group_iter(iterator, n=2):
    """ Given an iterator, it returns sub-lists made of n items
    (except the last that can have len < n)
    inspired by http://countergram.com/python-group-iterator-list-function"""
    accumulator = []
    for item in iterator:
        accumulator.append(item)
        if len(accumulator) == n: # tested as fast as separate counter
            yield accumulator
            accumulator = [] # tested faster than accumulator[:] = []
            # and tested as fast as re-using one list object
    if len(accumulator) != 0:
        yield accumulator

How would you have done it?

Have you ever needed to create a MySQL databases replication chain like A->B->C where B is slave of A and master of C? Me neither, until yesterday.

Since it took us about an afternoon to make it works (along with our DBAs, so we're not alone ;)) let's share some knowledge.

A very brief recap of how MySQL replication works:

1. slave I/O thread connects to the master, gets the new information from the binlog files and stores them in the relay log;
2. slave SQL thread reads the relay log and applies the changes to the slave database, without changing the slave binlog files.

As you probably know, Shani is our pet hedgehog. We finally managed to setup a blog just for her (sorry, it's in italian only), and also we uploaded tons of her photos.

You don't remember her? Here's a cute reminder:

Just when I was looking for a contact email to ask news about EuroPython 2011 dates... I noticed they are already there!! June 19 to 26 !