A Getter That Estimates: Class Variables, None, and datetime

Why does letting `get_calories` estimate a missing value force a class variable and datetime objects into the class?

Finger exercises

Short drills on what this video just taught. Write the code, run the checks, and reveal the answer only if you are stuck.

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Exercise 1 of 5

A rate every instance can reach

Every Swim burns 500 calories per hour, and that one rate is shared by every swim ever created — nothing ever changes it. Add it to the class below as a class variable named cal_per_hr, in the class body and outside every method. The checks read Swim.cal_per_hr and read the same name on an instance.

class Swim(object):
    """A class to keep track of swims"""

    # Class variable: the calories-per-hour rate for every swim
    ...

    def __init__(self, minutes):
        self.minutes = minutes

class Swim(object):
    """A class to keep track of swims"""

    # Class variable: the calories-per-hour rate for every swim
    ...

    def __init__(self, minutes):
        self.minutes = minutes

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the class carries the rate

an instance reaches the same rate

the rate lives on the class, not on each instance

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