quiz4-17.py

# -----------------
# User Instructions
# 
# Write a function, path_cost, which takes a path as input 
# and returns the total cost associated with that path. 
# Remember that paths will obey the convention
# path = [state, (action, total_cost), state, ...] 
#
# If a path is less than length 3, your function should
# return a cost of 0.

def path_cost(path):
    """The total cost of a path (which is stored in a tuple
    with the final action."""
    # path = [state, (action, total_cost), state, ... ]
    if len(path) < 3:
        return path[1][1]
    else:
        result = path[1::2]
        result = reversed(result)
        return result.next()[1]
        
def bcost(action):
    """Returns the cost (a number) of an action in the
    bridge problem."""
    # An action is an (a, b, arrow) tuple; a and b are 
    # times; arrow is a string. 
    a, b, arrow = action
    return max(a,b)

def test():
    assert path_cost(('fake_state1', ((2, 5, '->'), 5), 'fake_state2')) == 5
    assert path_cost(('fs1', ((2, 1, '->'), 2), 'fs2', ((3, 4, '<-'), 6), 'fs3')) == 6
    assert bcost((4, 2, '->'),) == 4
    assert bcost((3, 10, '<-'),) == 10
    return 'tests pass'

print test()