python __str__ 用于对象

Question

在试图弄清楚 BeautifulSoup 的工作原理时，我偶然学习了 __str__ 方法(我是 python 新手)。因此，如果我没有误解，那么 __str__ 方法有助于确定类在打印出来时的表示方式。例如:

class Foo:
    def __str__(self):
        return "bar"

>>> x = Foo()
>>> print x
bar

对吗？所以断言我是对的，是否可以覆盖字典列表的 __str__ 方法？我的意思是说在 Foo 类中你有:

class Foo:
   def __init__(self):
      self.l = [{"Susan": ("Boyle", 50, "alive")}, {"Albert": ("Speer", 106, "dead")}]

现在有可能得到以下结果吗？

>>> x = Foo()
>>> print x.l
"Susan Boyle is 50 and alive. Albert Speer is 106 and dead."

编辑

考虑到 agf 的解决方案，我怎样才能再次访问字典？我的意思是，如果我定义 __str__ 方法，那么显然我应该定义其他东西来按原样检索字典。请考虑以下示例:

class PClass(dict):
    def __str__(self):
        # code to return the result that I want 

class Foo:
    def __init__(self):
        self.l = PClass({"Susan": ["Boyle", ........ })

>>> x = Foo()
>>> print x.l 
# result that works great
>>> y = x.l["Susan"] # this would not work. How can I achieve it? 

Answer 1

您需要对要打印的项目进行子类化。

from itertools import chain

class PrintableList(list): # for a list of dicts
    def __str__(self):
        return '. '.join(' '.join(str(x) for x in
            chain.from_iterable(zip((item[0], 'is', 'and'), item[1])))
                for item in (item.items()[0] for item in self)) + '.'

class PrintableDict(dict): # for a dict
    def __str__(self):
        return '. '.join(' '.join(str(x) for x in
            chain.from_iterable(zip((item[0], 'is', 'and'), item[1])))
                for item in self.iteritems()) + '.'

class Foo:
   def __init__(self):
      self.d = PrintableDict({"Susan": ("Boyle", 50, "alive"), 
                              "Albert": ("Speer", 106, "dead")})

class Bar:
   def __init__(self):
      self.l = PrintableList([{"Susan": ("Boyle", 50, "alive")}, 
                              {"Albert": ("Speer", 106, "dead")}])

foo = Foo()
print self.d
bar = Bar()
print self.l