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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def browse(self, folder, levels=None, prefix=None):
 """ Returns the directory tree of the global model. Directories are always JSON objects (map/dictionary), and files are always arrays of modification time and size. The first integer is the files modification time, and the second integer is the file size. Args: folder (str):
 The root folder to traverse. levels (int):
 How deep within the tree we want to dwell down. (0 based, defaults to unlimited depth) prefix (str):
 Defines a prefix within the tree where to start building the structure. Returns: dict """

        assert isinstance(levels, int) or levels is None
        assert isinstance(prefix, string_types) or prefix is None
        return self.get('browse', params={'folder': folder,
                                          'levels': levels,
                                          'prefix': prefix})