new year, new blog: spreading the word with tekuti

December 23, 2010

This will be my last post in wordpress.com after using the service since 2006. At the time of this writing the blog has received 27122 visits which is not very much, but at least it means someone is reading (…may be the crawlers?).

WordPress is provided with statistics, anti spam filters, themes and much more (that I do not really use)… So, why am I leaving? Simply, because I want to learn new things (I’ve been feeling quite stuck lately). But, shouldn’t I be worried with the “what” instead of the “how”? Like solving the problem instead of worrying about the language I use? Well, I guess so, but I like to learn new languages even I don’t solve any problem (at the end this is not true, but I don’t want to get recursive here).

My new blog (http://hacks-galore.org/aleix/blog) is based on tekuti, a weblog software written in Scheme, using Git as its persistent store. All axelio’s posts have been imported to the new blog, so don’t panic!

Happy hacking!

ropemacs and remote files (fuse)

November 16, 2010

This morning I needed to edit some python scripts from a local server at work and, as always, used the TRAMP Emacs mode, but immediately found a problem. A few months ago I installed the great python refactoring library rope and its Emacs mode ropemacs. It comes out that ropemacs asks you for the location of your rope project if it cannot find it (this always happens the first time you start a project).

TRAMP URLs look like this:

/ssh:user@server:/path

So, you can now imagine what happens when Emacs gives an URL like this to rope (which is a python library and doesn’t know anything about TRAMP URLs) as if it was a local file name…

Traceback (most recent call last):
  ...
  ...
  File "/usr/lib/python2.6/.../ropemode/interface.py", line 88, in open_project
    self.project = rope.base.project.Project(root)
  File "/usr/lib/python2.6/.../rope/base/project.py", line 134, in __init__
    os.mkdir(self._address)
OSError: [Errno 2] No such file or directory: '/ssh:user@server:/path'

The worst is that you are continuously being asked by Emacs to enter a valid rope project location.

The solution? Simply use the FUSE SSH Filesystem.

$ sudo apt-get install sshfs
$ sshfs user@server:path mountpoint

FUSE stands for Filesystem in Userspace. With FUSE you will end up editing remote files as if they were in your computer and the great thing is that you don’t need root access, so any user can mount a FUSE filesystem.

Update 2010/11/17: FUSE mounted directory can be unmounted with:

$ fusermount -u mountpoint

Land of Lisp: Come back here, you cowards!

October 29, 2010

I must admit it, I just don’t know Common Lisp, nor Scheme, nor any other Lisp dialect, only some notions and ideas. However, I’ve been always fascinated with the people behind them and with their defense on what they say is the most powerful and beautiful programming language. Articles, user groups, books, conferences… and basically a lot of fun.

Today, even I do not understand most of the articles in LtU, I read about the Land of Lisp. Check out the music video and interactive comic (note: this is not for everyone).

More on easy acronyms generation

October 22, 2010

About four years ago I posted an article about easy acronyms generation in LaTeX. Yesterday, I did some updates to the script (tex-acronyms.py) that I wanted to share with you (if anyone is reading…). Basically, the updates are:

  • A user defined acronyms file can be specified via the -u argument. User defined acronyms take precedence over global acronyms definition.
  • Global excluded acronyms file has been removed. Now, the user must define acronyms to be excluded in the user defined acronyms file as an empty acronym. For example:

    \nomenclature{GHH}{}
    

    Then, the definition of GHH will not be included in the list of acronyms.

  • To facilitate the read of acronyms conflicts, it is now specified if the conflict is because of a “Duplicated“, “Undefined” or “Excluded” acronym.

So, the script is called as before but a new optional argument -u can be specified for the user defined acronyms file:

tex-acronyms.py [-r] -d /path/to/acronyms \
                -i article.tex \
                [-u user_acronyms.tex] \
                -o acronyms.tex \
                -e acronyms.errors

BitPacket: Python 2.x and 3.0 compatibility

October 14, 2010

Lately, I’ve been porting BitPacket to Python 3.0. I wanted to keep backwards compatibility with Python 2.6 (which is the 2.x I have in my Debian) and, thankfully, I only had to fix three minor issues:

  • Unicode strings
  • Dictionary keys
  • Bytes vs. strings

StringIO and unicode strings

If you have ever used the StringIO module you should be familiar with this:

try:
    from cStringIO import StringIO
except ImportError:
    from StringIO import StringIO

In Py3k the StringIO is located under the io package, so you should changed the above by:

from io import StringIO

which is also compatible with Python 2.6.

Once I did the change my code only worked in Py3k, Python 2.6 complained when trying to use the write method with a simple string:

>>> from io import StringIO
>>> stream = StringIO()
>>> stream.write("test")
Traceback (most recent call last):
  File "", line 1, in 
  File "/usr/lib/python2.6/io.py", line 1515, in write
    s.__class__.__name__)
TypeError: can't write str to text stream

You should note that in Py3k all the strings are unicode strings by default. This is not true in Python 2.6, so my first approach was the following:

>>> stream.write(u"test")
4

Unfortunately, this only worked in Python 2.6. Py3k does not recognize the unicode prefix “u“, giving you this error:

>>> stream.write(u"test")
  File "", line 1
    stream.write(u"test")
                       ^
SyntaxError: invalid syntax

I googled a bit and find out a Making code compatible with Python 2 and 3 post (from the guy that finished all the SICP exercices) where it explained some similar issues, so I came up with this solution:

def u_str(string):
    if sys.hexversion >= 0x03000000:
        return string
    else:
        return unicode(string)

>>> stream.write(u_str("test"))
4

In Py3k, unicode does not exist but as that line is never executed we don’t get any error.

Even that worked well, I was not very happy with it. It was too slow and I had to use the custom u_str function everywhere. So, I googled a bit more and I found a nice pycon 2009 talk about Python 3.0 compatibility. Finally, I had which I think is the best solution (for both speed and clearness):

try:
    # This will raise an exception in Py3k, as unicode doesn't exist
    str = unicode
except:
    pass

So, instead of defining a new u_str function, the str type is re-defined as unicode for Python 2.6. Then, I only had to update all the strings in the code to use str:

>>> stream.write(str("test"))
4

Note: I put this code in a compatibility.py file and import it everywhere I need it.

Dictionary keys

The next problem was reported by the 2to3 tool that comes with Py3k.

-                for k in field.keys():
+                for k in list(field.keys()):

Basically, it told me that the dictionary keys() method returns a view in Py3k not a list, so it needs to be converted to a list as explained here:

dict methods dict.keys(), dict.items() and dict.values() return “views” instead of lists. For example, this no longer works: k = d.keys(); k.sort(). Use k = sorted(d) instead (this works in Python 2.5 too and is just as efficient).

Bytes vs. strings

Finally, the last issue was about the difference between strings and bytes in Python 2.x and 3.0. In Python 2.x, bytes is just an alias for str:

>>> bytes
<type 'str'>

In Py3k, bytes and str are different classes and behave differently, see below:

>>> s = "AB"
>>> s[0]
'A'
>>> s[1]
'B'
>>> b = b"AB"
>>> b[0]
65
>>> b[1]
66

This means that one needs to take care of functions returning bytes (e.g. struct.pack) and the operations performed with the returned data, in my case a call to the ord function, that failed with the typical error message:

TypeError: ord() expected string of length 1, but int found

So, following the approaches mentioned above I added the following function to my compatibility.py:

def u_ord(c):
    if sys.hexversion >= 0x03000000:
        return c
    else:
        return ord(c)

which I used instead of the built-in ord in the struct.pack case.

Hope this helps to someone.

Happy hacking!


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