Trying to understand a very simple class - from the book "dive into python"

[walterbyrd]

Example 5.6. Coding the FileInfo Class
class FileInfo(UserDict):
    "store file metadata"
    def __init__(self, filename=None):
        UserDict.__init__(self)        (1)
        self["name"] = filename        (2)


What I do not understand is the last line. I thought 'self' was
supposed to refer to an instance of the object. But the square
brackets seem to indicate a list. Except you can not assign values to
a list like that. So where does "name" come from?

I am sure this is totally simple, but I missing something.