Solve a discrete constraint satisfaction problem to open the portcullises at the end of the Soultaker's Pit in Avernum 5.

avernum5-soultaker.py

#!/usr/bin/env python2

from collections import Counter
from constraint import * # <https://pypi.python.org/pypi/python-constraint>

class S(object):
    Red = "red"
    Blue = "blue"
    Green = "green"
    Nonsparkling = "nonsparkling"
    Absent = "absent"

class L(object):
    NW = "NW"
    NE = "NE"
    SW = "SW"
    SE = "SE"

states = (S.Red, S.Blue, S.Green, S.Nonsparkling, S.Absent)
sparkling = (S.Red, S.Blue, S.Green)
locations = (L.NW, L.NE, L.SW, L.SE)

p = Problem()
for location in locations:
    p.addVariable(location, states)

# At least one stand to the north has no orb.
p.addConstraint(
    lambda nw, ne: (nw == S.Absent) or (ne == S.Absent),
    (L.NW, L.NE))

# A western orb has red sparkles.
p.addConstraint(
    lambda nw, sw: (nw == S.Red) or (sw == S.Red),
    (L.NW, L.SW))

# There are no blue sparkles.
p.addConstraint(
    NotInSetConstraint({S.Blue}))

# A sparkling orb to the north is not red.
p.addConstraint(
    lambda nw, ne: (nw in sparkling and not nw == S.Red) or (ne in sparkling and not ne == S.Red),
    (L.NW, L.NE))

# No sparkles are the same color
p.addConstraint(
    lambda *args: all(Counter(args)[state] <= 1 for state in sparkling),
    locations)

# Two orbs are sparkling on the diagonal
p.addConstraint(
    lambda nw, ne, sw, se: (nw in sparkling and se in sparkling) or (ne in sparkling and sw in sparkling),
    (L.NW, L.NE, L.SW, L.SE))

print(p.getSolutions())