如何输出前面有正号和零的整数

def format_integer(num):
    if num > 0:
        sign = '+'
    else:
        sign = ''
    
    if num == 0:
        zero = '0'
    else:
        zero = ''
    
    return sign + zero + str(num)

# 示例用法
num = 123
formatted_num = format_integer(num)
print(formatted_num)  # 输出：+123

num = -456
formatted_num = format_integer(num)
print(formatted_num)  # 输出：-456

num = 0
formatted_num = format_integer(num)
print(formatted_num)  # 输出：+0