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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 headers(self):
 """ Returns a list of the last HTTP response headers. Header keys are normalized to capitalized form, as in `User-Agent`. """

    headers = self.conn.issue_command("Headers")
    res = []
    for header in headers.split("\r"):
      key, value = header.split(": ", 1)
      for line in value.split("\n"):
        res.append((_normalize_header(key), line))
    return res