<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def decode(var, encoding):
 """ If not already unicode, decode it. """

    if PY2:
        if isinstance(var, unicode):
            ret = var
        elif isinstance(var, str):
            if encoding:
                ret = var.decode(encoding)
            else:
                ret = unicode(var)
        else:
            ret = unicode(var)
    else:
        ret = str(var)
    return ret