导入类和定义类之间的python区别

Question

我想在实例的一些参数之间创建依赖关系（不一定与示例中的类相同）。我想出了以下代码，直到我决定将它移到模块中并通过导入来使用它。

class objectD(object):
  def __init__(self,val1,val2,val3):
    self.val1 = val1
    self.val2 = val2
    self.val3 = val3

  def __str__(self):
    return str(str(self.val1)+","+str(self.val2)+","+str(self.val3))

  def dependence(self,dependent):
    print "values val1 and val2 of "+str(self)+" now depend on "+dependent
    self.val1 = eval(dependent).val1
    self.val2 = eval(dependent).val2
    self.dependent = dependent

  def update(self):
    self.val1 = eval(self.dependent).val1
    self.val2 = eval(self.dependent).val2

#test
obj1 = objectD(350,4,500)
print obj1
obj2 = objectD(230,1,1000)
print obj2
obj2.dependence("obj1")#problem with imported class occurs there
print obj2
obj1.val1 = 1315
obj1.val2 = 6464
print obj1
obj2.update()
print obj2

问题似乎在于将依赖项分配给实例，根据 python，使用类的导入版本根本不存在。在我看来，对实例的调用方法依赖（）在模块中而不是在我的脚本中进行。 有没有办法以某种方式修复导入，或者可能有一些不同的方法来创建依赖项？

Answer 1

应该不需要eval。为什么不直接这样做呢？

class objectD(object):
  def __init__(self,val1,val2,val3):
    self.val1 = val1
    self.val2 = val2
    self.val3 = val3

  def __str__(self):
    return str(str(self.val1)+","+str(self.val2)+","+str(self.val3))

  def dependence(self,dependent):
    print "values val1 and val2 of "+str(self)+" now depend on "+dependent
    self.val1 = dependent.val1
    self.val2 = dependent.val2
    self.dependent = dependent

  def update(self):
    self.val1 = self.dependent.val1
    self.val2 = self.dependent.val2

#test
obj1 = objectD(350,4,500)
print obj1
obj2 = objectD(230,1,1000)
print obj2
obj2.dependence(obj1)#problem with imported class no longer occurs there
print obj2
obj1.val1 = 1315
obj1.val2 = 6464
print obj1
obj2.update()
print obj2

这将按预期工作，因为dependent 仅存储对obj1 的引用，而不是对象本身的状态。所以对update() 的调用实际上会提取新值。