补全代码def nextDate(year, month, day): if year < 1900 or year > 9999: # 检查年份是否合法 return "Invalid year!" if month < 1 or month > 12: # 检查月份是否合法 return "Invalid month!" if day < 1 or day > 31: # 检查天数是否合法 return "Invalid day!" if month == 2: # 处理2月份 if year % 4 == 0 and (year % 100 != 0 or year % 400 == 0): # 闰年 if day > 29: return "Invalid day!" else: if day > 28: return "Invalid day!" elif month in [4, 6, 9, 11]: # 处理只有30天的月份 if day > 30: return "Invalid day!" # 计算下一天日期 if day == 31: if month == 12: return str(year + 1) + "-01-01" else: return str(year) + "-" + str(month + 1).zfill(2) + "-01" elif day == 30: if month == 4 or month == 6 or month == 9 or month == 11: return str(year) + "-" + str(month + 1).zfill(2) + "-01" else: return str(year) + "-" + str(month).zfill(2) + "-" + str(day + 1).zfill(2) elif day == 29 and month == 2: if year % 4 == 0 and (year % 100 != 0 or year % 400 == 0): return str(year) + "-03-01" else: return "Invalid day!" elif day == 28 and month == 2: if year % 4 == 0 and (year % 100 != 0 or year % 400 == 0): return str(year) + "-" + str(month).zfill(2) + "-" + str(day + 1).zfill(2) else: return str(year) + "-03-01" else: return str(year) + "-" + str(month).zfill(2) + "-" + str(day + 1).zfill(2)并让他成为一个可执行的程序

这段代码已经可以作为一个可执行的程序，你可以将它保存为一个.py文件。以下是完整的代码：

def nextDate(year, month, day):
    if year < 1900 or year > 9999: # 检查年份是否合法
        return "Invalid year!"
    if month < 1 or month > 12: # 检查月份是否合法
        return "Invalid month!"
    if day < 1 or day > 31: # 检查天数是否合法
        return "Invalid day!"
    
    if month == 2: # 处理2月份
        if year % 4 == 0 and (year % 100 != 0 or year % 400 == 0): # 闰年
            if day > 29:
                return "Invalid day!"
        else:
            if day > 28:
                return "Invalid day!"
    elif month in [4, 6, 9, 11]: # 处理只有30天的月份
        if day > 30:
            return "Invalid day!"
    
    # 计算下一天日期
    if day == 31:
        if month == 12:
            return str(year + 1) + "-01-01"
        else:
            return str(year) + "-" + str(month + 1).zfill(2) + "-01"
    elif day == 30:
        if month == 4 or month == 6 or month == 9 or month == 11:
            return str(year) + "-" + str(month + 1).zfill(2) + "-01"
        else:
            return str(year) + "-" + str(month).zfill(2) + "-" + str(day + 1).zfill(2)
    elif day == 29 and month == 2:
        if year % 4 == 0 and (year % 100 != 0 or year % 400 == 0):
            return str(year) + "-03-01"
        else:
            return "Invalid day!"
    elif day == 28 and month == 2:
        if year % 4 == 0 and (year % 100 != 0 or year % 400 == 0):
            return str(year) + "-" + str(month).zfill(2) + "-" + str(day + 1).zfill(2)
        else:
            return str(year) + "-03-01"
    else:
        return str(year) + "-" + str(month).zfill(2) + "-" + str(day + 1).zfill(2)

# 测试
print(nextDate(2021, 9, 30)) # 2021-10-01
print(nextDate(2021, 2, 28)) # 2021-03-01
print(nextDate(2020, 2, 28)) # 2020-02-29
print(nextDate(1900, 2, 29)) # Invalid day!
print(nextDate(10000, 2, 28)) # Invalid year!