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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 get_revisions(page):
 """Extract the revisions of a page. Args: page: a string Returns: a list of strings """

  start_string = "    <revision>\n"
  end_string = "    </revision>\n"
  ret = []
  current_pos = 0
  while True:
    start_pos = page.find(start_string, current_pos)
    if start_pos == -1:
      break
    end_pos = page.find(end_string, start_pos)
    assert end_pos != -1
    ret.append(page[start_pos + len(start_string):end_pos])
    current_pos = end_pos + len(end_string)
  return ret