Encode to ucs-2 by using utf_16_be then checking for invalid results

ucs2.py

# -*- coding: utf-8 -*-
from __future__ import unicode_literals
from __future__ import print_function
import struct

def CheckUcs2BEIsValid(e, big_endian=True):
	#UCS-2 is a fixed width encoding. Therefore, check that the
	#variable width aspect of UTF-16 is not used.
	if big_endian:
		struct_code = ">H"
	else:
		struct_code = "<H"

	for i in range(len(e))[::2]:
		val = struct.unpack(struct_code, e[i:i+2])[0]
		val2 = (val & 0xfc00)
		if val2 in [0xd800, 0xdc00]:
			raise ValueError("UTF-16 detected")

def CheckUcs2BEIsValid_Method2(e, s_len):
	#UCS-2 is a fixed width encoding. Therefore, check that the
	#variable width aspect of UTF-16 is not used.

	if len(e) != s_len*2:
		raise ValueError("Variable width detected")

if __name__=="__main__":
	tests = ["abc$", "день€", "𐐷", "😀"]

	for s in tests:	
		try:
			#UTF-16 is an extension of UCS-2, so start by using that encoding
			e = s.encode("utf_16_be")

			#Then check the result is valud UCS-2
			CheckUcs2BEIsValid(e)
			print ("{} is ok".format(s))
		except ValueError as err:
			print ("{} in {}, this isn't valid UCS-2".format(err, s))

	for s in tests:	
		try:
			e = s.encode("utf_16_le")
			CheckUcs2BEIsValid(e, False)
			print ("{} is ok".format(s))
		except ValueError as err:
			print ("{} in {}, this isn't valid UCS-2".format(err, s))

	for s in tests:	
		try:
			e = s.encode("utf_16_be")
			CheckUcs2BEIsValid_Method2(e, len(s))
			print ("{} is ok".format(s))
		except ValueError as err:
			print ("{} in {}, this isn't valid UCS-2".format(err, s))