## more oop examples:

# metrocard:

class metrocard:
    
    def __init__(self,initval):
        self.value = initval
        self.price = 2.5      # $2.50 per ride
    # constructor

    def ride(self):  # take one ride
        if self.value>=self.price:
            self.value -= self.price
            return "please watch the gap between the train and the platform"
        else:
            return "not enough funds"
    # ride

    def refill(self,amt): # refill card, $1 credit for every 10 dollars
        self.value += amt
        if (amt>=10):
            self.value += int(amt) / 10
    # refill

    def check(self):  # check current balance:
        return self.value
    # check

    def renew(self): # transfer balance to a new card
        newcard = metrocard(self.value)
        self.value = 0
        return newcard
    # renew
#metrocard

mycard = metrocard(20)
card2 = metrocard(15)
print mycard.ride()
print "your current value is ", mycard.check()

mycard2 = mycard.renew()
print mycard.ride()
print mycard2.ride()
mycard.refill(25)


#### minutes and seconds

class time:

    def __init__(self,m,s):  # constructor sets intial time
        self.min = m
        self.sec = s  
    # __init__

    def reset(self):
        self.min, self.sec = 0,0
    #reset

    # destructive addition of minutes and seconds:
    def add(self,m,s):
        tsec = self.sec + s
        self.min += m + (tsec/60)
        self.sec = tsec % 60
    #time

    # version of add that accepts one additional parameter:

    def sum(self,other):
        tsec = self.sec + other.sec
        self.min += other.min + (tsec/60)
        self.sec = tsec % 60
    # sum

    # non-destructive version of add, returns a new time object:

    def cadd(self,other):
        tsec = self.sec + other.sec
        m = self.min + other.min + (tsec/60)
        s = tsec % 60
        newtime = time(m,s)
        return newtime
    # constructive addition

    ### defining a function in terms of other functions

    def tick(self):   # destructive increase of one second
        self.add(0,1)
    # tick

    def equals(self,other):
        return self.min == other.min and self.sec == other.sec
    # ==  : recommend against overloading __eq__


    ### OPERATOR OVERLOADING:  

    def __add__(self,other):   # overloads +
        tsec = self.sec + other.sec
        m = self.min + other.min + (tsec/60)
        s = tsec % 60
        newtime = time(m,s)
        return newtime
    # constructive addition

    def __cmp__(self,other):  # overloads ==, <, >=, etc ...
        sec1 = self.min*60 + self.sec
        sec2 = other.min*60 + other.sec
        return sec1-sec2
    # cmp returns negative if self<other, positive if self>other, 0 otherwise

    def tostring(self):
        return str(self.min)+"m"+str(self.sec)+"s"
    # tostring
# time

t1 = time(1,30)
t2 = time(2,45)
t1.add(0,3)   
t2.sum(t1)
t3 = t1.cadd(t2)
t2.tick()
t4 = t1 + t2    # using __add__ implicitly
print t1.tostring()
print t2.tostring()
print t3.tostring()
print t4.tostring()

t5 = time(1,33)
print t1, t5
print (t1 == t5)  # false without operator overloading!
print t1.equals(t5)
print t1 <= t5