David,
Somehow, you have not installed the module in python. Do the last three commands again, capture the output and post it here.
BP
pi@raspberrypi:~/SDL_Pi_SmartGardenSystem/SDL_Pi_8PixelStrip $ cd python
pi@raspberrypi:~/SDL_Pi_SmartGardenSystem/SDL_Pi_8PixelStrip/python $ sudo apt-get install python-dev swig
Reading package lists... Done
Building dependency tree
Reading state information... Done
python-dev is already the newest version (2.7.16-1).
swig is already the newest version (3.0.12-2).
0 upgraded, 0 newly installed, 0 to remove and 362 not upgraded.
pi@raspberrypi:~/SDL_Pi_SmartGardenSystem/SDL_Pi_8PixelStrip/python $ sudo python ./setup.py install
running install
running bdist_egg
running egg_info
writing rpi_ws281x.egg-info/PKG-INFO
writing top-level names to rpi_ws281x.egg-info/top_level.txt
writing dependency_links to rpi_ws281x.egg-info/dependency_links.txt
reading manifest file 'rpi_ws281x.egg-info/SOURCES.txt'
writing manifest file 'rpi_ws281x.egg-info/SOURCES.txt'
installing library code to build/bdist.linux-armv7l/egg
running install_lib
running build_py
creating build
creating build/lib.linux-armv7l-2.7
copying neopixel.py -> build/lib.linux-armv7l-2.7
running build_ext
building '_rpi_ws281x' extension
swigging rpi_ws281x.i to rpi_ws281x_wrap.c
swig -python -o rpi_ws281x_wrap.c rpi_ws281x.i
creating build/temp.linux-armv7l-2.7
arm-linux-gnueabihf-gcc -pthread -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fno-strict-aliasing -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-9NJ3qw/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security -fPIC -I/usr/include/python2.7 -c rpi_ws281x_wrap.c -o build/temp.linux-armv7l-2.7/rpi_ws281x_wrap.o
arm-linux-gnueabihf-gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions -Wl,-z,relro -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-9NJ3qw/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security -Wl,-z,relro -Wdate-time -D_FORTIFY_SOURCE=2 -g -fdebug-prefix-map=/build/python2.7-9NJ3qw/python2.7-2.7.16=. -fstack-protector-strong -Wformat -Werror=format-security build/temp.linux-armv7l-2.7/rpi_ws281x_wrap.o -L../. -lws2811 -lrt -o build/lib.linux-armv7l-2.7/_rpi_ws281x.so
/usr/bin/ld: cannot find -lws2811
collect2: error: ld returned 1 exit status
error: command 'arm-linux-gnueabihf-gcc' failed with exit status 1
pi@raspberrypi:~/SDL_Pi_SmartGardenSystem/SDL_Pi_8PixelStrip/python $