import base64                                                       

a = base64.b64encode(bytes(u’complex string: ñáéíóúÑ’, «utf-8»))

# a: b’Y29tcGxleCBzdHJpbmc6IMOxw6HDqcOtw7PDusOR’

b = base64.b64decode(a).decode(«utf-8», «ignore»)                   

print(b)

# b :complex string: ñáéíóúÑ