类实例覆盖属性

Question

我用Python写了一个用于计算的类，它看起来像：

default = {…}
class Case(object):
    def __init__(self, name, wt, wd, ft, bc, burnup, cr_state):
        self.name = name
        self.burnup = burnup
        self.infn = 'fa-'+faType+'-'+str(self.burnup)+'-'+self.name
        self.data = default
        self.data['caseName'] = name
        self.data['water-temp'] = str(wt)
        self.data['water-den'] = str(wd)
        self.data['fuel-temp'] = str(ft)
        self.data['boron-con'] = str(bc)
        self.cr_state = cr_state
        self.data['cr_state'] = cr_state
        self.data['burnup'] = str(burnup)

实际上，它实现了更多的方法，但这应该足以说明。

问题是，当我尝试创建此类的不同实例时，它们具有相同的属性，例如：

basis = Case('basis', 578.0, 0.71614, 578.0, 0.00105, 0, 'empty')
wt450 = Case('wt450', 450.0, 0.71614, 578.0, 0.00105, 0, 'empty')

在此之后，如果我检查：

print basis.data == wt450.data

它返回True .问题的根源在哪里？

Answer 1

就像 jonrsharpe 的评论一样，您可以使用 'dict.copy 方法复制default字典的内容。

class Case(object):
    def __init__(self, name, wt, wd, ft, bc, burnup, cr_state):
        self.name = name
        self.burnup = burnup
        self.infn = 'fa-'+faType+'-'+str(self.burnup)+'-'+self.name
        # Copy the content of the dict
        self.data = default.copy()
        # Overwrite data's default values
        self.data['caseName'] = name
        self.data['water-temp'] = str(wt)
        self.data['water-den'] = str(wd)
        self.data['fuel-temp'] = str(ft)
        self.data['boron-con'] = str(bc)
        self.cr_state = cr_state
        self.data['cr_state'] = cr_state
        self.data['burnup'] = str(burnup)

或者，如果要使值与默认值保持同步，则可以创建一个方法，该方法将从实例中获取值，如果找不到值，则使用默认字典上的值。它看起来像这样：

class Case(object):
    def __init__(self, name, wt, wd, ft, bc, burnup, cr_state):
        self.name = name
        self.burnup = burnup
        self.infn = 'fa-'+faType+'-'+str(self.burnup)+'-'+self.name
        # We create a NEW dictionary to hold the overwritten values
        self.data = {}
        # Write data to OUR OWN dict
        self.data['caseName'] = name
        self.data['water-temp'] = str(wt)
        self.data['water-den'] = str(wd)
        self.data['fuel-temp'] = str(ft)
        self.data['boron-con'] = str(bc)
        self.cr_state = cr_state
        self.data['cr_state'] = cr_state
        self.data['burnup'] = str(burnup)
    def property(name):
        """
        Return the value of `name`, if name wasn't defined, then use the
        value from default.
        """
        # Return the property from our own dict. If it can't find the property
        # then get it from the default dict. If the property doesn't exists
        # returns None.
        return self.data.get(name, default.get(name))
# Then
print basis.property('caseName') == wt450.property('caseName')
> False