There were a few types available and I picked up 3 different ones: warm white LEDs on a flexible but fairly rigid wire, some brighter white LEDs encapsulated in a snowflake housing and some traditional multi-colour LEDs.
The strings of LEDs come attached to two AA cells in a neat enclosure with an on/off switch. I snipped the wires fitted jumper wire housings to the end of each so I could plug them straight onto the GPIO header. As the LEDs run on 3v and I was intending to drive them using an 'expendable' model B, I decided not to bother with a series resistor.
I kept the batteries and the holders - these are bound to be useful for other projects (similar boxes can cost almost as much as the whole LED set).
Then I knocked up a quick Python program to run a mixed illuminate sequence for each of the lights.
from gpiozero import PWMLED
from time import sleep
white = PWMLED(23)
snowflakes = PWMLED(18)
colours = PWMLED(25)
LIGHTS = [white,snowflakes,colours]
for x in range(1,100):
lights.value = x/100
for i in LIGHTS:
t = threading.Thread(target=sequence, args=(i,))
I then added a line to the /etc/rc.local file on the Pi so that the Python code runs automatically at startup.
Our Christmas tree was already quite covered with decorations so I decided to use these new lights on our spiky cactus!