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python-3.xclassdatetimeinstance-variables

how to use datetime objects in a class instance?


An instance of the Rabbit class is created in a for loop and given a datetime object as init variable but all instances get the same datetime value. I expected a time difference for each instance; what am I missing in understanding here?

from datetime import datetime
class Rabbit_birth:
    num_eyes = 2  # <- Class variable
    num_legs = 4
    num_ears = 2
    num_tails = 1
    num_of_rabbits = 0

    def __init__(self, name = 'Rabbit',
                 fur_colour = 'unknown',
                 eye_colour = 'unknown',
                 sex = 'unsexed',
                 breed = 'unknown',
                 dob = datetime.now(),
                 tob = datetime.now()
                 ):

        self.name = name  # <- Instance variable
        self.fur_colour = fur_colour
        self.eye_colour = eye_colour
        self.sex = sex
        self.breed = breed
        self.dob = str(dob.strftime("%x"))
        self.tob = str(tob.strftime("%X"))
        Rabbit_birth.num_of_rabbits += 1


    def display_rabbit(self):
        dob_time = self.dob+" at "+self.tob
        return ("{0.name} is a {0.sex} rabbit"
    " and has {0.fur_colour} fur and "
    "{0.eye_colour} eyes, {0.name} is "
    "of the {0.breed} breed of rabbits.\n"
    "{0.name}'s DOB is ").format(self) + dob_time         
################################################
print()

print('Number of rabbits is ',Rabbit_birth.num_of_rabbits)





rabbits=[]
def create_rabbit():
    lr=[]
    rabbit = ('name', 'fur colour', 'eye colour', 'sex', 'breed')
    for item in rabbit:
        r = input(item+' >')
        lr.append(r)
    r0,r1,r2,r3,r4=lr
    name = Rabbit_birth(r0,r1,r2,r3,r4)    
    return name
for i in range(3):

    name=create_rabbit()
    rabbits.append(name)
    print(rabbits[i].display_rabbit())

Solution

  • I see the mistake I have made, it's a matter of passing the datetime object in the wrong scope.

    Here is the relevant corrected code:

    ## <- class experiment
    from datetime import datetime
    class Rabbit_birth:
        num_eyes = 2  # <- Class variable
        num_legs = 4
        num_ears = 2
        num_tails = 1
        num_of_rabbits = 0
    
        def __init__(self, name = 'Rabbit',
                     fur_colour = 'unknown',
                     eye_colour = 'unknown',
                     sex = 'unsexed',
                     breed = 'unknown',
                     dob = None, # This line changed
                     tob = None  # This line changed
                     ):
            self.name = name  # <- Instance variable
            self.fur_colour = fur_colour
            self.eye_colour = eye_colour
            self.sex = sex
            self.breed = breed
            self.dob = datetime.now() # This line changed
            self.tob = datetime.now() # This line changed
            Rabbit_birth.num_of_rabbits += 1
    
    
        def display_rabbit(self):
            # This line below changed
            dob_time = str(self.dob.strftime("%x"))+" at "+str(self.tob.strftime("%X"))
            return ("{0.name} is a {0.sex} rabbit"
        " and has {0.fur_colour} fur and "
        "{0.eye_colour} eyes, {0.name} is "
        "of the {0.breed} breed of rabbits.\n"
        "{0.name}'s DOB is ").format(self) + dob_time         
    ################################################