code: def from_string(cls, public_key):
          
          public_key_data = _helpers.to_bytes(public_key)
  
          if _CERTIFICATE_MARKER in public_key_data:
              cert = cryptography.x509.load_pem_x509_certificate(
                  public_key_data, _BACKEND)
              pubkey = cert.public_key()
  
          else:
              pubkey = serialization.load_pem_public_key(
                  public_key_data, _BACKEND)
  
          return cls(pubkey)
docs: Construct an Verifier instance from a public key or public
          certificate string.
  
          Args:
              public_key (Union[str, bytes]): The public key in PEM format or the
                  x509 public key certificate.
  
          Returns:
              Verifier: The constructed verifier.
  
          Raises:
              ValueError: If the public key can't be parsed.