input: Write a python function to extract email addresses from a given string using regex.
  assert extract_emails("Please contact us at support@example.com for further information.") == ["support@example.com"]
  assert extract_emails("Our emails are joe@example.com and admin@domain.org.") == ["joe@example.com", "admin@domain.org"]
  assert extract_emails("No email here!") == []
output: def extract_emails(text):
      import re
      return re.findall(r'[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}', text)