Package is installed but EmulatorLock('sense_emu') is false

[DarkSky7]

pip install sense_emu sense_hat
both say that those packages are already installed AND
sense_emu and sense_hat directories are definitely present in $PYTHON_HOME/lib/site-packages/
but... in sense_hat.py
lock = EmulatorLock('sense_emu') // line 89
if not lock.wait(1): // line 90, enables
warnings.warn(Warning('No emulator detected; spawning sense_emu_gui')) // line 91

The packages are clearly present, the code is being run from the sense_emu directory (via 'from sense_emu import SenseHat' in the source file)

Packages are installed, but the lock fails. I'm not sure what's wrong here. Suggestions?