<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def is_unary_operator(oper):
 """returns True, if operator is unary operator, otherwise False"""

    # definition:
    # member in class
    # ret-type operator symbol()
    # ret-type operator [++ --](int)
    # globally
    # ret-type operator symbol( arg )
    # ret-type operator [++ --](X&, int)
    symbols = ['!', '&', '~', '*', '+', '++', '-', '--']
    if not isinstance(oper, calldef_members.operator_t):
        return False
    if oper.symbol not in symbols:
        return False
    if isinstance(oper, calldef_members.member_operator_t):
        if len(oper.arguments) == 0:
            return True
        elif oper.symbol in ['++', '--'] and \
                isinstance(oper.arguments[0].decl_type, cpptypes.int_t):
            return True
        return False

    if len(oper.arguments) == 1:
        return True
    elif oper.symbol in ['++', '--'] \
            and len(oper.arguments) == 2 \
            and isinstance(oper.arguments[1].decl_type, cpptypes.int_t):
        # may be I need to add additional check whether first argument is
        # reference or not?
        return True
    return False