我正试图按照this page中的代码和解释,为约束满足问题(CSP)开发一个框架。我的Python版本是2.7.13,所以我不得不稍微修改代码(我不能在这台计算机上进行更新或下载)。见下表:
from abc import ABCMeta
class abstractclassmethod(classmethod):
__isabstractmethod__ = True
def __init__(self, callable):
callable.__isabstractmethod__ = True
super(abstractclassmethod, self).__init__(callable)
class Constraint(object):
def __init__(self, variables):
self.variables = variables
@abstractclassmethod
def satisfied(self, assignment):
pass
class CSP(Constraint):
def __init__(self, variables, domains):
self.variables = variables
self.domains = domains
self.constraints = {}
for variable in self.variables:
self.constraints[variable] = []
if variable not in self.domains:
raise LookupError("Every variable should have a domain assigned to it")
def add_constraint(self, constraint):
for variable in constraint.variables:
if variable not in self.variables:
raise LookupError("Variable in constraint not in CSP")
else:
self.constraints[variable].append(constraint)
def consistent(self, variable, assignment):
for constraint in self.constraints[variable]:
if not constraint.satisfied(assignment):
return False
return True
def backtracking_search(self, assignment):
if len(assignment) == len(self.variables):
return assignment
for v in self.variables:
if v not in assignment:
unassigned.append(v)
first = unassigned[0]
for value in self.domains[first]:
local_assignment = assignment[:] # we make a copy
local_assignment[first] = value
if self.consistent(first, local_assignment):
result = self.backtracking_search(local_assignment)
if result is not None:
return result
return None
class MapColoringConstraint(Constraint):
def __init__(self, place1, place2):
self.place1 = place1
self.place2 = place2
super(Constraint, self).__init__()
def satisfied(sef, assignment):
if self.place1 not in assignment or self.place2 not in assignment:
return True
return assignment[self.place1] != assignment[self.place2]
我正在用澳大利亚地图着色问题测试这个框架(如上面的链接所示)
if __name__ == "__main__":
variables = ["Western Australia", "Northern Territory", "South Australia",
"Queensland", "New South Wales", "Victoria", "Tasmania"]
domains = {}
for variable in variables:
domains[variable] = ['red', 'green', 'blue']
csp = CSP(variables, domains)
csp.add_constraint(MapColoringConstraint("Western Australia", "Northern Terriroty"))
csp.add_constraint(MapColoringConstraint("Western Australia", "South Australia"))
csp.add_constraint(MapColoringConstraint("South Australia", "Northern Territory"))
csp.add_constraint(MapColoringConstraint("Queensland", "Northern Territory"))
csp.add_constraint(MapColoringConstraint("Queensland", "South Australia"))
csp.add_constraint(MapColoringConstraint("Queensland", "New South Wales"))
csp.add_constraint(MapColoringConstraint("New South Wales", "South Australia"))
csp.add_constraint(MapColoringConstraint("Victoria", "South Australia"))
csp.add_constraint(MapColoringConstraint("Victoria", "New South Wales"))
csp.add_constraint(MapColoringConstraint("Victoria", "Tasmania"))
solution = csp.backtracking_search()
if solution is None:
print("No solution found!")
else:
print(solution)
我经常遇到以下错误:
File 'csp.py', line 33, in add_constraint
for variable in constraint.variables:
AttributeError: 'MapColoringConstraint' object has no attribute 'variables'
除了一些修改,我的代码应该是相同的网页上。我似乎忽略了一些东西或删除了一些我不应该。有人能帮我找出缺了什么吗?你知道吗
在父类的init()方法上调用super()方法的地方,问题是
super(Constraint, self).__init__()
,这不会将父变量属性赋给子类,因此当add_constraint()
方法尝试获取属性时,它会抛出您指示的错误。你知道吗您可以阅读有关pythons继承层次结构的更多信息,以了解更多信息this article is good。你知道吗
我已经做了一些参考文章和更新代码如下,它应该能够运行预期。你知道吗
样品运行
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