python 时间计算器的问题

Question

下面是自己写的一段时间计算的代码，要求相加，相减，和乘法计算
output如下要求：
the first time interval (fti) is hours=21, minutes=58, seconds=50
the second time interval (sti) is hours=1, minutes=45, seconds=22
the expected result of addition (fti + sti) is 23:44:12
the expected result of subtraction (fti - sti) is 20:13:28
the expected result of multiplication (fti * 2) is 43:57:40
然后问题来了，根据题目要求要用到__str__(self) method, 我现在这段代码只能output后三行，像第一和第二行怎么用__str__来执行？我试过但只能print出一行，还有最后一个乘法的小时怎么变成非标准时间格式，因为用的时间格式都是"%H:%M:%S"，所以最后一行小时的显示达不到要求


```python
from datetime import time, datetime
class time_interval:
    def __init__(self,hours,minutes,seconds):
        self.hours=hours
        self.minutes=minutes
        self.seconds=seconds
    #def __str__(self):
     #   return "the first time interval (fti) is hours=%d, minutes=%d, seconds=%d"%(self.hours,self.minutes,self.seconds)+"
    def __add__(self,others):
        x=self.seconds+others.seconds
        y=self.minutes+others.minutes
        z=self.hours+others.hours
        if x > 59:
            x = x-60
            y += 1
            if y > 59:
                y = y-60
                z += 1
                if z > 23:
                    z = z-24
        if y > 59:
            y = y-60
            z += 1
            if z > 23:
                z=z-24
        if z > 23:
            z=z-24
        return "the expected result of addition (fti+sti) is "+time(z,y,x).strftime("%H:%M:%S")
    def __sub__(self,others):
        x=self.seconds-others.seconds
        y=self.minutes-others.minutes
        z=self.hours-others.hours
        if x < 0:
            x = 60+x
            y -= 1
            if y < 0:
                y = 60+y
                z -= 1
                if z < 0:
                    z = 24+z
        if y < 0:
            y = 60+y
            z -= 1
            if z < 0:
                z=24+z
        if z < 0:
            z=z+24
        return "the expected result of subtraction (fti-sti) is "+time(z,y,x).strftime("%H:%M:%S")
    def __mul__(self,var):
        x=self.seconds*var
        y=self.minutes*var
        z=self.hours*var
        if x > 59:
            x = x-60
            y += 1
            if y > 59:
                y = y-60
                z += 1
                if z > 23:
                    z = z-24
        if y > 59:
            y = y-60
            z += 1
            if z > 23:
                z=z-24
        if z > 23:
            z=z-24
        return "the expected result of multiplication (fti*2) is "+time(z,y,x).strftime("%H:%M:%S")
p1=time_interval(21,58,50)
p2=time_interval(1,45,22)
print(p1.__add__(p2))
print(p1.__sub__(p2))
print(p1.__mul__(2))

```

Answer 1

可以用静态属性记录实例化了多少个实例，然后建立一个数组来得到数字对应的英文内容
输出非标准时间，直接输出小时，分钟和秒就行，而且注意小时不要添加大于23的天进位操作，直接累加就行

'''
下面是自己写的一段时间计算的代码，要求相加，相减，和乘法计算
output如下要求：
the first time interval (fti) is hours=21, minutes=58, seconds=50
the second time interval (sti) is hours=1, minutes=45, seconds=22
the expected result of addition (fti + sti) is 23:44:12
the expected result of subtraction (fti - sti) is 20:13:28
the expected result of multiplication (fti * 2) is 43:57:40
然后问题来了，根据题目要求要用到__str__(self) method, 我现在这段代码只能output后三行，像第一和第二行怎么用__str__来执行？
我试过但只能print出一行，还有最后一个乘法的小时怎么变成非标准时间格式，因为用的时间格式都是"%H:%M:%S"，所以最后一行小时的显示达不到要求
 '''
 

from datetime import time, datetime
class time_interval:
    instancenum=0
    chrs=['first','second']#更多数组对照英文增加这里的数组
    def __init__(self,hours,minutes,seconds):
        self.hours=hours
        self.minutes=minutes
        self.seconds=seconds
        print(self.__str__())
        time_interval.instancenum+=1
    def __str__(self):
        #(time_interval.chrs[time_interval.instancenum%len(time_interval.chrs)] 这里意思是超过chrs长度后从头开始取对应
        return "the %s time interval (fti) is hours=%d, minutes=%d, seconds=%d"%(time_interval.chrs[time_interval.instancenum%len(time_interval.chrs)],self.hours,self.minutes,self.seconds)
    def __add__(self,others):
        x=self.seconds+others.seconds
        y=self.minutes+others.minutes
        z=self.hours+others.hours
        if x > 59:
            x = x-60
            y += 1
            if y > 59:
                y = y-60
                z += 1
                if z > 23:
                    z = z-24
        if y > 59:
            y = y-60
            z += 1
            if z > 23:
                z=z-24
        if z > 23:
            z=z-24
        return "the expected result of addition (fti+sti) is "+time(z,y,x).strftime("%H:%M:%S")
    def __sub__(self,others):
        x=self.seconds-others.seconds
        y=self.minutes-others.minutes
        z=self.hours-others.hours
        if x < 0:
            x = 60+x
            y -= 1
            if y < 0:
                y = 60+y
                z -= 1
                if z < 0:
                    z = 24+z
        if y < 0:
            y = 60+y
            z -= 1
            if z < 0:
                z=24+z
        if z < 0:
            z=z+24
        return "the expected result of subtraction (fti-sti) is "+time(z,y,x).strftime("%H:%M:%S")
    def __mul__(self,var):
        x=self.seconds*2
        y=self.minutes*2
        z=self.hours*2
        if x > 59:
            x = x-60
            y += 1
            if y > 59:
                y = y-60
                z += 1
                #if z > 23:
                #    z = z-24
        if y > 59:
            y = y-60
            z += 1
            #if z > 23:
            #    z=z-24
        #if z > 23:
        #    z=z-24
        return "the expected result of multiplication (fti*2) is %d:%d:%d"%(z,y,x)#.strftime("%H:%M:%S")

p1=time_interval(21,58,50)
p2=time_interval(1,45,22)
p3=time_interval(1,45,22)
print(p1.__add__(p2))
print(p1.__sub__(p2))
print(p1.__mul__(2))