我在Python shell上检查了几个例子，它们似乎吐出了相同的数字。但是在一个需要近似大量数字的程序中，它们显然会产生不同的结果。
我正在试着写一个小程序来模拟一个物体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
正如你所看到的，我使用int()方法和随机生成器"random.randrange"来实现它。
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，这两段代码产生完全不同的结果。我想知道为什么会这样。Int()和floor()对于正数应该具有相同的效果，并且这两个随机函数似乎产生相似的数字。
好吧，我不知道你的问题的答案-我怀疑他们返回完全相同的东西。然而，我认为你的解决方案有一个问题，可能会解释输出:
在"cleanTileAtPosition"
self.cleaned.append((int(pos.getX()), int(pos.getY())))
In 'getNumCleanedTiles'
return len(self.cleaned)
这段代码似乎允许一个tile被清理多次。这不是你的老师代码所做的，因为瓷砖只能设置为"True"一次。
(顺便说一下，因为随机。Randrange返回一个整数。整数转换不应该做任何事情!)
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int型，所以这应该不是问题。
你们的方法有一个很大的不同。random.randrange返回一个整数，在位置上调用int()。你在处理整数。同时，random.random() * something返回一个浮点数，math.floor也返回一个浮点数。你的老师一直在和花车打交道。
这至少是int和math.floor之间的差异，但我不知道为什么这会产生完全不同的结果。你能说得更具体一点吗?
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'>
尽管int()和floor()对正整数做"同样的事情"，但结果是不同的类型。这可能会导致各种不同的交互，这取决于您稍后对它们进行的操作。Python将从它的角度找出如何使它"工作"，尽管它不一定会给你想要的结果。
一般来说，当你在编程中做任何数学运算时，你都希望你使用的类型保持一致，这样你就不必担心类型转换和提升以及所有那些讨厌的东西。
用"整数"代替数学。尽管如此，Python在浮点数<->整数比较中有足够的黑魔法，因此这个差异在上面的代码中应该没有问题。然而，这两个版本的代码都带有明显的Java或c++"重音"，这使得它比简单的Python代码要复杂得多。差异很可能出现在代码的其他点上，而不是在这次四舍五入上。例如-尝试使用random.randint而不是获得浮点数，然后四舍五入，以。