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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 cat(self, multihash, offset=0, length=-1, **kwargs):
 r"""Retrieves the contents of a file identified by hash. .. code-block:: python Traceback (most recent call last):
 ipfsapi.exceptions.Error: this dag node is a directory b'<!DOCTYPE html>\n<html>\n\n<head>\n<title>ipfs example viewer</…' Parameters multihash : str The path to the IPFS object(s) to be retrieved offset : int Byte offset to begin reading from length : int Maximum number of bytes to read(-1 for all) Returns ------- str : File contents """

        opts = {}
        if offset != 0:
            opts['offset'] = offset
        if length != -1:
            opts['length'] = length
        args = (multihash,)
        return self._client.request('/cat', args, opts=opts, **kwargs)