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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 _escape_token(token, alphabet):
 r"""Replace characters that aren't in the alphabet and append "_" to token. Apply three transformations to the token: 1. Replace underline character "_" with "\u", and backslash "\" with "\\". 2. Replace characters outside of the alphabet with "\###;", where ### is the character's Unicode code point. 3. Appends "_" to mark the end of a token. Args: token: unicode string to be escaped alphabet: list of all known characters Returns: escaped string """

  token = token.replace(u"\\", u"\\\\").replace(u"_", u"\\u")
  ret = [c if c in alphabet and c != u"\n" else r"\%d;" % ord(c) for c in token]
  return u"".join(ret) + "_"