Question

我有一组类，它们的属性之一是url。我想建立一个这个类的字典，由该URL键入。这是我提出的代码：

class pagesByUrl(dict):
    "a cross reference of pages by url rather than object name"
    def __init__(self):
        pages={}
        for page in dir(xxxPages):
            try:
                pgAttr=getattr(xxxPages, page)
                pg=pgAttr('dummybrowser')
                pages[pg.url] = page
            except (KeyError, TypeError, AttributeError):
                pass
        print pages #At this point, the dictionary is good.
        self=pages
        print self #Also here, still just what I want.




pg=pagesByUrl()
print "pg is:", pg #But here, pg is an empty dictionary.

如果要将此类实例化为我想要的字典，我该怎么办？

Answer 1

class pagesByUrl(dict):
    "a cross reference of pages by url rather than object name"
    def __init__(self):
        dict.__init__(self) #!
        pages={}
        for page in dir(xxxPages):
            try:
                pgAttr=getattr(xxxPages, page)
                pg=pgAttr('dummybrowser')
                pages[pg.url] = page
            except (KeyError, TypeError, AttributeError):
                pass

       self.update(pages)
       #Alternatively, forgo the previous `dict.__init__(self)` and the 
       #previous line and do:
       #dict.__init__(self,pages)

如果您执行self = pages，则只需使用self字典替换__init__函数中的本地名称pages即可。你实际上并没有改变self的字典。

当然，此时，根本不需要pages字典 - 我们可以使用self：

class pagesByUrl(dict):
    "a cross reference of pages by url rather than object name"
    def __init__(self):
        dict.__init__(self)
        for page in dir(xxxPages):
            try:
                pgAttr=getattr(xxxPages, page)
                pg=pgAttr('dummybrowser')
                self[pg.url] = page
            except (KeyError, TypeError, AttributeError):
                pass

Answer 2

如果你想拥有纯粹的“类型字典”，请查看实例创建的__new__()方法

class dictA(dict):
    def __new__(self):
        self._pages={"one":1, "two":2}
        return self._pages

class pagesByUrl(dict):
    def __init__(self):
        _pages = {"one":1, "two":2}
        dict.__init__(self)
        self.update(_pages)

d = {"one":1, "two":2}
print type(d)
print d

d = dictA()
print type(d)
print d

d = pagesByUrl()
print type(d)
print d

输出：

<type 'dict'>
{'two': 2, 'one': 1}
<type 'dict'>
{'two': 2, 'one': 1}
<class '__main__.pagesByUrl'>
{'two': 2, 'one': 1}

通过每个类的属性创建类名字典

2 个答案: