input: Write a function to extract all email addresses from a given string using a regular expression. If no email addresses are found, return an empty list.
  assert find_emails("This is an example with two emails: john@example.com, and jane@example.com")==['john@example.com', 'jane@example.com']
  assert find_emails("No email address here.")==[]
  assert find_emails("")==[]
  assert find_emails("Check these emails: alice@domain.com and bob@example.net")==['alice@domain.com', 'bob@example.net']
  assert find_emails("Invalid email: john@.com")==[]
output: import re
  
  def find_emails(text):
      pattern = r'[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}'
      return re.findall(pattern, text)