python类的内建方法

研究email源码学到的

class test():
    """Class for generating text/* type MIME documents."""

    def __init__(self):
        self._headers = []

    def __getitem__(self, name, failobj=None):
        name = name.lower()
        for k, v in self._headers:
            if k.lower() == name:
                return v
        return failobj

    def __setitem__(self, name, val):
        self._headers.append((name, val))

    def __str__(self):
        """Return the entire formatted message as a string.
        This includes the headers, body, and envelope header.
        """
        return self.as_string()

    def as_string(self):
        return self._headers

test1=test()
test1['1']=2
print test1.as_string()