函數的可選參數組-python

Question

好的，所以我必須制作兩個類（在兩個不同的腳本中），兩個類都稱為Block，用於存儲有關矩形塊的位置和大小的信息。 版本1應該具有屬性，以存儲塊中心的坐標（作為單獨的x坐標和y坐標或成對的數字*）以及塊的寬度和高度。 版本2應該具有存儲左下角（“ SW”角）的坐標和右上角（“ NE”角）的坐標的屬性。

因此，我知道如何分別為每個對象設置構造函數，但是對於此分配，兩個版本都應具有一個構造函數，該構造函數將采用中心的一對坐標以及寬度和高度（作為浮點數），或者兩對坐標，分別代表該塊的兩個相對角。 這是我到目前為止嘗試過的：

class Block:
    """Stores information about the position and size of a rectangular block.

    Attributes: x-coordinate (int), y-coordinate (int), width (int), height (int) OR northeast corner (int) and southwest corner (int)"""

    def __init__(self, center = '', width = '', height = '', SW = '', NE = ''):
        """A constructor that assigns attributes to the proper variables

        Block, tuple, tuple -> None"""
        self.center = center
        self.width = width
        self.height = height
        self.SW = SW
        self.NE = NE

但我敢肯定，這實際上並沒有達到我想要的方式。 基本上，我需要能夠輸入一組變量作為中心，寬度和高度，或者我需要輸入兩個角。 有沒有辦法做到這一點？

Answer 1

您必須檢查將哪些參數傳遞給函數並采取相應的措施。 通常，您要做的是選擇一種規范表示形式來實際存儲數據，並讓__init__將傳遞給它的所有參數轉換為規范形式。 例如：

# Use None to represent missing data. Think about it: "hello" is not a 
# valid width; neither is "".
def __init__(self, center=None, width=None, height=None, SW=None, NE=None):
    """A constructor that assigns attributes to the proper variables

    Block, tuple, tuple -> None"""

    if center is not None and width is not None and height is not None:
        # If either SW or NE is given, ignore them 
        self.center = center
        self.width = width
        self.height = height
    elif SW is not None and NE is not None:
        # _convert_corners is a helper function you define
        self.center, self.width, self.height = _convert_corners(SW, NE)
    else:
        # Not entirely true. Give width, height, and one corner, you
        # could reconstruct the center, but this is just an example.
        raise ValueError("Insufficient information to construct Block")

您可以使用屬性即時計算其他屬性，而不必冗余地存儲它們：

@property
def SW(self):
    # return the south-west corner as computed from
    # self.center, self.height, and self.width

@property
def NE(self):
    # return the north-east corners computed from
    # self.center, self.height, self.width

另一種方法是使用類方法來提供備用構造函數。

def __init__(self, center, width, height):
    "Define a block by its center, width, and height"
    self.center = center
    self.width = width
    self.height = height

@classmethod
def from_corners(self, sw, ne):
    "Define a block by two corners"
    c, w, h = _convert_corners(sw, ne)
    return Block(c, w, h)

正在使用：

# For demonstration purposes, I'm assuming points like the center
# and the corners are simple tuples of integer coordinates
b1 = Block((10, 50), 5, 7)
b2 = Block.from_corners((20, 30), (40, 70))

Answer 2

你快到了 試試這樣的東西...

class Block:
    def __init__(self, center = '', width = '', height = '', SW = '', NE = ''):
        if SW != ''  or  NE != '':
            if SW == ''  and  NE ==  '':   # usage error
                return None                # throw an exception here
            self.center = getCenterFromCorners(SW, NE)  # ((sw[0]+ne[0])/2, ...)
            self.width = getWidthFromCorners(SW, NE)    # abs(sw[0]-ne[0])
            self.height = getHeightFromCorners(SW, NE)  # abs(sw[1]-ne[1])
        else:
            if center == ''  or  width == ''  or '' height == '':
                return None                # throw exception
            self.center = center
            self.width = width
            self.height = height
        return self

# usage: block1 and block2 should be similar
block1 = Block(center=(10,20), height=2, width=4)
block2 = Block(SW=(9,18), NE=(11,22))

我確定您可以替換getCenterFromCorners（）的代碼，...