From the pyshp README:

• bbox, mbox and zbox attributes are all new Namedtuples.

Namedtuples don't have tolist(), calling list() on shapefile._Array (pyshp < 3.0.0) and tuple (pyshp >= 3.0.0) produces the same result.

Fixes: #632

Ah. I was about to say "Hey, when I installed basemap, pyshp was downgraded". Time to monitor this PR!