Writes to a mutable file in the MFS.

        .. code-block:: python

            >>> c.files_write("/test/file", io.BytesIO(b"hi"), create=True)
            b''

        Parameters
        ----------
        path : str
            Filepath within the MFS
        file : io.RawIOBase
            IO stream object with data that should be written
        offset : int
            Byte offset at which to begin writing at
        create : bool
            Create the file if it does not exist
        truncate : bool
            Truncate the file to size zero before writing
        count : int
            Maximum number of bytes to read from the source ``file``

def files_write(self, path, file, offset=0, create=False, truncate=False,
                    count=None, **kwargs):
        """Writes to a mutable file in the MFS.

        .. code-block:: python

            >>> c.files_write("/test/file", io.BytesIO(b"hi"), create=True)
            b''

        Parameters
        ----------
        path : str
            Filepath within the MFS
        file : io.RawIOBase
            IO stream object with data that should be written
        offset : int
            Byte offset at which to begin writing at
        create : bool
            Create the file if it does not exist
        truncate : bool
            Truncate the file to size zero before writing
        count : int
            Maximum number of bytes to read from the source ``file``
        """
        opts = {"offset": offset, "create": create, "truncate": truncate}
        if count is not None:
            opts["count"] = count
        kwargs.setdefault("opts", opts)

        args = (path,)
        body, headers = multipart.stream_files(file, self.chunk_size)
        return self._client.request('/files/write', args,
                                    data=body, headers=headers, **kwargs)