Teaching the Snake a New Trick

I learned Python about three years ago. At that time, I didn't know Python at all and took a job with a company that uses Python extensively. My job didn't actually consist of any Python work, but since I liked the company, I knew learning Python would be important for getting rehired. Python has since grown on me quite a bit, and whenever I am given a programming problem, I often find I come up with a Python solution the fastest. There are a few things that I love about it, but I'm not here to start a language war. I just taught the snake a new trick and I want to share it with you.

First, some background. I am a huge fan of the functional programming syntax that Python provides. Its for loops and list manipulation helpers are particularly natural and it's never been easier to mix and match imperative and functional programming.

One thing that I have been trying to do for a while but never actually found a Good Solution (TM) to is iterating over each consecutive pair of elements in a list. For example, if the list contains [1, 2, 3, 4], I want to execute some block of code with the pairs (1, 2), (2, 3), (3, 4).

The naive solution looks something like this:

L = [1, 2, 3, 4]

for i in range(len(L) - 1):

  a, b = L[i], L[i + 1]

  # work with a, b here

But come on, how ugly is that?

A much nicer solution uses the zip function as follows:

for a, b in zip(L[:-1], L[1:]):

  # work with a, b here

This forms two lists, one with the last element chopped off and one which is missing its first element. The pairs of corresponding elements of these two lists are the pairs of consecutive elements in the original list (zip does this part). Neat, huh? Can anyone come up with an even cleaner solution?

I leave you with a quote about programmers from Tidbits from the Dungeon:

Programmers are in a race with the Universe to create bigger and better idiot-proof programs, while the Universe is trying to create bigger and better idiots. So far the Universe is winning. -- Rich Cook

Well, it's back to homework for me.

-Cat

Lenovo Battery Sudden Death Syndrome

I'm a proud owner of a Lenovo ThinkPad X61s notebook. I bought it just over a year ago and I've been thoroughly happy with it. Until a month ago.

On October 16, two days after the end of my battery's one-year warranty, I came home after leaving the laptop plugged in during the entire day and, without thinking twice, unplugged the AC adapter as I usually do to take the laptop to the couch. The laptop turned off instantly and would not power back up with the battery. The ThinkPad Power Manager had this to say:

With the battery connected, the battery light on the front of the laptop flashed rapidly orange (it's supposed to be flashing green when charging and solid green when finished charging). Note that this happened suddenly -- the day before this happened, I had about 4 to 5 hours of battery life as usual.

I immediately called customer support and was greeted by a polite yet very unhelpful man. He was unable to help me in any way because my warranty had expired 2 days prior. It's a little silly, but I don't blame him; he's just following company policy. It looked like I would have to figure this out on my own.

From what I had heard, one of the most common causes of failure of Lithium-based batteries is failure of one of the cells (this battery pack, for example, is made up of 8 cells). The charging circuitry then avoids charging or discharing the cell, since damaged Lithium cells can be quite dangerous (explosions, etc.). Sometimes, it's as easy as replacing that cell; failed cells typically have a very low voltage, usually lower than 1.5V.

So, what does a good reverse engineer do with a potentially repairable battery pack? He cracks it open. WARNING: DON'T DO THIS AT HOME. It could literally blow up in your face.

Here's what a ThinkPad X61s 92P1172 battery looks like inside:

At this point, it's worth noting how the cells are connected in such a battery. The 8 cylindrical cells (part number "LH7M2D8") are grouped into 4 pairs. The two cells in each pair are in parallel, while the pairs are in series. If the cell voltage is Vcell, then the total voltage Vtotal = 4 * Vcell.

I measured each of the cell (pair) voltages, and they were all approximately 3.97V. According to TI's Using NiMH and Li-Ion in Portable Applications (Figure 1), this is a normal voltage for a mostly-charged cell. In fact, the Power Manager applet showed a total voltage of 15.86V, which adds up. However, it's debatable whether the PM reading should be trusted, since, not knowing exactly how the PM works, there is a possibility that the battery is in fact damaged and the reading is stale data from when it was last healthy. Either way, my multimeter confirmed the cells have a healthy voltage (I don't know enough about Li cells to say for sure that this means the cells are completely healthy). I also haven't tried measuring their voltage under load (a small resistor), since that's fairly dangerous if not done properly and I would prefer to avoid any fires until it becomes absolutely necessary.

And this is about where I got stuck. All signs so far point to a defective charge controller or a corrupted controller nonvolatile memory. I have tried doing the "reset battery gauge" procedure in Power Manager, but that results in my laptop hard-crashing (powering off) and nothing happens to the battery. I'm quite open to suggestions.

Thanks for reading, see you next time! :-)

Better iTap Learning

iTap (or T9 for you Nokia fans out there) is a widespread predictive text technology for cell phones, typically used when composing text messages (SMS). Each key on a cell phone's keypad is labelled with 3 (or 4) letters and, as you're pressing one number at a time, the phone tries to figure out which permutation of the sets of letters is most likely to be the word you are writing.

Of course, it always helps to integrate your own personal touch: new predictive text technologies actually learn from the words that you type. The newest versions even go so far as to record combinations of words and propose them to you when you're typing in case you want to repeat the same phrase. Very helpful stuff. But all this is done only based on what you write.

But what if the cell phone were to learn from your received text messages as well? Chances are you and your friends' vocabularies are pretty close. This potentially doubles the amount of learning material and therefore doubles the learning speed. Also, by associating the learned information with a particular correspondent, the device can make intelligent choices about the words it proposes to you. (You probably didn't mean to text "whats up dawg" to your mom.)

Motorola, hire me so I can implement this for you.