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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 SignFiles(self, filenames):
 """Signs multiple files at once."""

    file_list = " ".join(filenames)
    subprocess.check_call("%s %s" % (self._signing_cmdline, file_list))
    if self._verification_cmdline:
      subprocess.check_call("%s %s" % (self._verification_cmdline, file_list))