Slots in Python

Slots seem to be poorly documented. What they do is simple, but whether they are used is tricky. This is a little mini-post on slots.

Basics of Metaclasses

This is a quick tutorial over the basics of what metaclasses do.

The Metaclass¶

Metaclasses, while seemingly a complex topic, really just do something very simple. They control what happens when you have code that turns into a class object. The normal place they are executed is right after the class statement. Let's see that in action by using print as our metaclass.

Note: this post uses Python 3 metaclass notation. Python 2 uses assignment to a special __metaclass__ attribute to set the metaclass. Also, Python 2 requires explicit, 2 argument super() calls.

In [13]:

class WillNotBeAClass(object, metaclass=print):
    x=1

WillNotBeAClass (<class 'object'>,) {'x': 1, '__module__': '__main__', '__qualname__': 'WillNotBeAClass'}

Here, we have replaced the metaclass (type) with print, just to investigate how it works. This is quite useless, of course, but does show that the metaclass gets called with three arguments when a class is created. The first is the name of the class to be created, the second is a tuple of base classes, and the third is a dictionary that has the namespace of the body of a class, with a few extra special values added.

Factory Classmethods in Python

I haven't seen a great deal of practical documentation about using classmethods as factories in Python (which is arguably the most important use of a classmethod, IMO). This post hopes to fill in that gap.

Making a Plumbum Autoload Extension for IPython

I recently decided to try my hand at making an auto-load extension for Python and plumbum. I was planning to suggest it as a new feature, then I thought it might be an experimental feature, and now it's just a blog post. But it was an interesting idea and didn't seem to be well documented process on the web. So, here it is.

The plan was to make commands like this:

>>> from plumbum.cmd import echo
>>> echo("This is echoed!")

or

>>> from plumbum import local
>>> echo = local['echo']
>>> echo("This is echoed!")

into this:

>>> echo("This is echoed!")

Thereby making Plumbum even more like Bash for fast scripting.

Uncertainty Extension for IPython

Wouldn't it be nice if we had uncertainty with a nice notation in IPython? The current method would be to use raw Python,

In [1]:

from uncertainties import ufloat
print(ufloat(12.34,.01))

12.340+/-0.010

Let's use the handy infix library to make the notation easier. We'll define |pm| to mean +/-.

Note: this is a very simple library that is less than a page long. Feel free to write the code yourself (as I do later in this notebook).

Plumbum Color

I've been working on a color addition to Plumbum for a little while, and I'd like to share the basics of using it with you now. This library was originally built around a special str subclass, but now is built on the new Styles representation and is far more powerful than the first implementation. It safely does nothing if you do not have a color-compatible systems (posix + tty currently), but can be forced if need be. It is included with Plumbum, so you don't have to add a requirement for your scripts that is non-essential (as color often is). It is integrated with plumbum.cli, too. Also, I've managed to accelerate the color selection algorithims about 8x, allowing near game-like speeds. (see the fullcolor.py example).

University of Texas Doctoral Thesis Template

I have created a thesis class file for a UT Thesis in LaTeX. It has already been used for at least one passing thesis, so it does meet the current UT guidelines. (Please let me know if there are any issues!)

Since I use Bitbucket for all my private repositories (like my thesis itself), the code is in a Bitbucket repository rather than GitHub. Here is the link if you want to create a pull request or want to compile the class and documentation from the source .dtx file.

If all you want is a download of a working version, and if you don't want to compile the code but just want the class file, here are downloadable packages including the class file.