You were close; just try this instead:
all_selected = bottle.request.forms.getall('the_list')
You'll want to use request.forms and getall. request.forms
returns a MultiDict, which is the appropriate data structure for storing multiple selected options. getall
is how you retrieve the list of values from a MultiDict:
for choice in all_selected:
# do something with choice
or, more simply:
for selected in bottle.request.forms.getall('the_list'):
# do something with selected