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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 all_files(self):
 """ Returns a list of files known by the package manager """

        if self.files_command and not self.files:
            cmd = self.files_command
            files = shell_out(cmd, timeout=0, chroot=self.chroot)
            self.files = files.splitlines()
        return self.files