input: Write a python function to create a sitemap XML from a given URL.
  assert create_sitemap("http://example.com") == "sitemap.xml"
  assert os.path.exists("sitemap.xml") == True
output: import os
  from urllib.parse import urlparse
  from xml.etree.ElementTree import Element, SubElement, tostring, ElementTree
  
  def create_sitemap(url):
      urlset = Element("urlset", xmlns="http://www.sitemaps.org/schemas/sitemap/0.9")
      url_element = SubElement(urlset, "url")
      loc = SubElement(url_element, "loc")
      loc.text = url
  
      sitemap_xml = tostring(urlset, encoding="utf-8", method="xml")
      sitemap_path = "sitemap.xml"
  
      with open(sitemap_path, "wb") as file:
          file.write(sitemap_xml)
  
      return sitemap_path