理解Python类实例

Question

I'm working on a problem which uses a python class and has a constructor function to give the number of sides to one die and a function to roll the die with a random number returned based on the number of sides. I realize the code is very basic, but I'm having troubles understanding how to sum up the total of three rolled dice with different sides. Since a variable is passing the function instance what would be the best way to grab that value to add it up? Here is what I have.

*To clarify... I can get the totals of the roll1.roll_dice() to add up, but I have to show each roll individually and then the total of the three dice. I can do either one of those but not both.

class Die():

        def __init__(self, s = 6):
            self.sides = s
        def roll_die(self):
            x = random.randint(1,self.sides)
            return x

        roll1 = Die()   #Rolling die 1 with the default side of 6
        roll2 = Die(4)  #Rolling die 2 with 4 sides
        roll3 = Die(12) #Rolling die 3 with 12 sides

        print roll1.roll_die()  
        print roll2.roll_die()
        print roll3.roll_die()

Answer 1

You can store the results in a list:

rolls = [Die(n).roll_die() for n in (6, 4, 12)]

then you can show the individual results

>>> print rolls
[5, 2, 6]

or sum them

>>> print sum(rolls)
13

Or, instead, you could keep a running total:

total = 0
for n in (6, 4, 12):
    value = Die(n).roll_die()
    print "Rolled a", value
    total += value
print "Total is", total

(edited to reflect the changes/clarifications to the question)

Answer 2

I'm not sure exactly where you're confused. The simplest thing you need to do is separate the concept of a specific die you're going to roll (the object) with the action (rolling it). I would start here:

d6 = Die() #create die 1 with the default side of 6
d4 = Die(4) #create die 2 with 4 sides
d12 = Die(12) #create die 3 with 12 sides

roll1 = d6.roll_die()
roll2 = d4.roll_die()
roll3 = d12.roll_die()

print "%d\n%d\n%d\nsum = %d" % (roll1, roll2, roll3, roll1 + roll2 + roll3)

... and then get fancier with lists, etc.

Answer 3

It may also be useful to just store the last roll so you can get it whenever you want.

def __init__(self, s = 6):
    self.sides = s
    self.last_roll = None

def roll_die(self):
    self.last_roll = random.randint(1,self.sides)
    return self.last_roll

Answer 4

Since roll_die returns a value, you can add those values.

Try this.

roll1.roll_die() + roll2.roll_die()

What happens?

Answer 5

You can just sum the numbers. In case you want to sum the outcome of n rolls, consider adding this function to the class:

def sum_of_n_rolls(self, n)
    return sum(self.roll_die() for _ in range(n))

Also, consider renaming roll_die to just roll . It's obvious that it's not about rolling a rock, since the method is part of the class Die .

---

Edit : I now read you need to print intermediate rolls. Consider:

def n_rolls(self, n):
    return [self.roll_die() for _ in range(n)]

Now you can roll a 7-sided die 10 times:

rolls = Die(7).n_rolls(10)
print(rolls, sum(rolls))

Answer 6

Guess I'd do something like this:

# Create dice
sides = [6,4,12]
dice = [Die(s) for s in sides]

# Roll dice
rolls = [die.roll_die() for die in dice]

# Print rolls
for roll in rolls:
    print roll

You can also combine a few of these steps if you like:

for num_sides in [6,4,12]:
    print Die(num_sides).roll_die()

Answer 7

If I understood you correctly you want a class attribute.

UPDATE: Added a way for automatically reseting the total

import random

class Die():
    _total = 0

    @classmethod
    def total(cls):
        t = cls._total
        cls._total = 0
        return t

    def __init__(self, s=6):
        self.sides = s

    def roll_die(self):
        x = random.randint(1,self.sides)
        self.__class__._total += x
        return x

roll1 = Die()   #Rolling die 1 with the default side of 6
roll2 = Die(4)  #Rolling die 2 with 4 sides
roll3 = Die(12) #Rolling die 3 with 12 sides

print roll1.roll_die()  
print roll2.roll_die()
print roll3.roll_die()
print Die.total()
print "--"
print roll1.roll_die()  
print roll2.roll_die()
print roll3.roll_die()
print Die.total()

Answer 8

Let's get crazy :) (combined with my last answer as well)

class Die():
    def __init__(self, s = 6):
        self.sides = s
        self.last_roll = None

    def roll_die(self):
        self.last_roll = random.randint(1,self.sides)
        return self.last_roll

dice = map(Die, (6, 4, 12))
rolls = map(Die.roll_die, dice)

print rolls
print sum(rolls)