input: Write a function to extract all public email addresses from a given string. Return a list of email addresses found in the input string. If no email addresses are found, return an empty list. Note that the email addresses should be in the standard format such as 'user@domain.com'.
  def extract_emails(text):
    emails = re.findall(r"[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+", text)
    return emails
  
  assert extract_emails("My email is john@example.com and yours is john@gmail.com.") == ['john@example.com', 'john@gmail.com']
  assert extract_emails("Please contact support@company.org for more information.") == ['support@company.org']
  assert extract_emails("There are no emails in this string.") == []
  assert extract_emails("") == []
output: def extract_emails(text):
    emails = re.findall(r"[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+", text)
    return emails