Does the firmware determine that the pullups are missing and refuse to create the object? Will things work as expected once I attach the sensor and add the pullups?
I might have messed things up as I set up the environment on my iMac to recompile the firmware using the instructions on you site. That all worked well but I think that is when I started getting the error (I'm not positive though). I then reloaded the the original firmware back (Adafruit CircuitPython 4.0.0-alpha.5-497-g738e8f0). Problem remains.
How might I enable the pullups in code (I presume I can do this in python, right)?
The busio.I2C code that handles I2C should set the pull-ups on its own.
I'm not as familiar with the low-level details of the CircuitPython environment, so let me copy this thread over to the CircuitPython forum. The folks who moderate there know the code inside and out (because they wrote it).
Be aware that the Adafruit microcontroller boards do not have I2C pullup resistors built in! All of the Adafruit breakouts do, but if you're building your own board or using a non-Adafruit breakout, you must add 2.2K-10K ohm pullups on both SDA and SCL to the 3.3V.