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我检查了 Python shell 上的一些示例，它们似乎吐出了相同的数字。但是在一个应该对大量数字进行近似的程序中，它们显然会产生不同的结果。

我正在尝试编写一个小程序来模拟对象在矩形平面上的运动。为此，我必须编写一个名为“RectangularRoom”的类，它接受宽度和高度并创建一个网格：

class RectangularRoom(object):
"""
A RectangularRoom represents a rectangular region containing clean or dirty
tiles.

A room has a width and a height and contains (width * height) tiles. At any
particular time, each of these tiles is either clean or dirty.
"""
def __init__(self, width, height):
    """
    Initializes a rectangular room with the specified width and height.

    Initially, no tiles in the room have been cleaned.

    width: an integer > 0
    height: an integer > 0
    """
    self.width = width
    self.height = height
    self.room_coordinates = []
    for m in range(self.width):
        for n in range(self.height):
            self.room_coordinates.append((m,n))
    self.cleaned = []
def cleanTileAtPosition(self, pos):
    """
    Mark the tile under the position POS as cleaned.

    Assumes that POS represents a valid position inside this room.

    pos: a Position
    """
    self.cleaned.append((int(pos.getX()), int(pos.getY())))

def isTileCleaned(self, m, n):
    """
    Return True if the tile (m, n) has been cleaned.

    Assumes that (m, n) represents a valid tile inside the room.

    m: an integer
    n: an integer
    returns: True if (m, n) is cleaned, False otherwise
    """
    assert type (m)== int and type (n) == int
    return (m,n) in self.cleaned

def getNumTiles(self):
    """
    Return the total number of tiles in the room.

    returns: an integer
    """
    return self.width*self.height

def getNumCleanedTiles(self):
    """
    Return the total number of clean tiles in the room.

    returns: an integer
    """
    return len(self.cleaned)

def getRandomPosition(self):
    """ 
    Return a random position inside the room.

    returns: a Position object.
    """
    return Position (random.randrange(0 , self.width), random.randrange(0 , self.height))

def isPositionInRoom(self, pos):
    """
    Return True if pos is inside the room.

    pos: a Position object.
    returns: True if pos is in the room, False otherwise.
    """
    return (int(pos.getX()), int(pos.getY())) in self.room_coordinates

如您所见，我使用 int() 方法和随机生成器“random.randrange”实现了它。

在解决方案中，老师使用 math.floor() 函数和随机生成器 random.random() 实现了这个类：

class RectangularRoom(object):
"""
A RectangularRoom represents a rectangular region containing clean or dirty
tiles.

A room has a width and a height and contains (width * height) tiles. At any
particular time, each of these tiles is either clean or dirty.
"""
def __init__(self, width, height):
    """
    Initializes a rectangular room with the specified width and height.

    Initially, no tiles in the room have been cleaned.

    width: an integer > 0
    height: an integer > 0
    """
    self.width = width
    self.height = height
    self.tiles = {}
    for x in range(self.width):
        for y in range(self.height):
            self.tiles[(x, y)] = False

def cleanTileAtPosition(self, pos):
    """
    Mark the tile under the position POS as cleaned.

    Assumes that POS represents a valid position inside this room.

    pos: a Position
    """
    x = math.floor(pos.getX())
    y = math.floor(pos.getY())
    self.tiles[(x, y)] = True

def isTileCleaned(self, m, n):
    """
    Return True if the tile (m, n) has been cleaned.

    Assumes that (m, n) represents a valid tile inside the room.

    m: an integer
    n: an integer
    returns: True if (m, n) is cleaned, False otherwise
    """
    return self.tiles[(m, n)]

def getNumTiles(self):
    """
    Return the total number of tiles in the room.

    returns: an integer
    """
    return self.width * self.height

def getNumCleanedTiles(self):
    """
    Return the total number of clean tiles in the room.

    returns: an integer
    """
    return sum(self.tiles.values())

def getRandomPosition(self):
    """
    Return a random position inside the room.

    returns: a Position object.
    """
    return Position(random.random() * self.width,
                    random.random() * self.height)

def isPositionInRoom(self, pos):
    """
    Return True if pos is inside the room.

    pos: a Position object.
    returns: True if pos is in the room, False otherwise.
    """
    return ((0 <= pos.getX() < self.width)
            and (0 <= pos.getY() < self.height))

令人惊讶的是，这两段代码产生了完全不同的结果。我想知道为什么会这样。int() 和 floor() 应该对正数具有相同的效果，并且两个随机函数似乎产生相似的数字。

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4 回答 4

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好吧，我不知道你的问题的答案——我怀疑他们返回的东西完全相同。但是，我认为您的解决方案存在可能解释输出的问题：

在'cleanTileAtPosition'

self.cleaned.append((int(pos.getX()), int(pos.getY())))

在“getNumCleanedTiles”中

return len(self.cleaned)

此代码似乎允许多次清洁瓷砖。这不是您的教师代码所做的，因为磁贴只能设置为“真”一次。

（顺便说一句，因为 random.randrange 返回一个整数.. 整数转换应该什么都不做！）

编辑：另外 - 我认为类型差异值得考虑。但是你所有的类型都是“整数”，所以它不应该是一个问题。

于 2013-04-17T22:51:34.637 回答
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你的方法有一个很大的不同。random.randrange返回一个整数，然后调用int()位置。您正在使用整数。同时，random.random() * something返回一个浮点数，math.floor也返回一个浮点数。你的老师一直在使用花车。

这至少是 和 之间的区别int，math.floor但我不知道为什么会产生完全不同的结果。你能更具体一点吗？

于 2013-04-17T22:49:37.767 回答
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考虑以下示例：

>>> a = 1.2
>>> b = int(a)
>>> c = math.floor(a)
>>> b
1
>>> c
1.0
>>> type(c)
<type 'float'>
>>> type(a)
<type 'float'>
>>> type(b)
<type 'int'>

即使 int() 和 floor() 对正整数做“同样的事情”，结果却是不同的类型。这可能会导致各种不同的交互，具体取决于您稍后对它们执行的操作。Python 会从它的角度弄清楚如何让它“工作”，尽管它不一定会给你想要的结果。

通常，在编程中进行任何类型的数学运算时，您都希望使用的类型保持一致，这样您就不必担心类型转换和提升以及所有那些讨厌的事情。

于 2013-04-17T22:50:50.940 回答
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Using "integers" instead of math.floor terhe would be better - still, Python has enough black magic in float <-> integer comparisons that this difference alone should be no problem in the code above. The code however, in both versions has a distinct Java or C++ "accent" making it much more complictaed than simple Python code can be. It is likely the difference arises in some other point of the code - not on this rounding. For example - try using random.randint instead of getting a float and later rounding it, to start with.

于 2013-04-17T22:49:15.857 回答