在python中使用迭代器比较函数中的两个元素

Question

我是 python 新手，在理解和使用类中的迭代器时遇到一个小问题。

def findLargest(shapes):
"""
Returns a tuple containing the elements of ShapeSet with the
   largest area.
shapes: ShapeSet
"""
bestName = shapes.List[:]
for i in shapes.List:
    if i.cmp(i+1)== -1:
        bestName.remove(memo)
    if i.cmp(i+1)==1:
        bestName.remove(i)
for element in bestName:
    stringout=''
    stringout= stringout + 'Element ' + str(element.name) + ' with an area of ' + str(element.area()) + ', '
return stringout

所以基本上，我想比较元素列表的面积并获得面积最大的元素元组。我的问题是将我的元素“i”与元素“i+1”进行比较。我不知道怎么称呼它。为了迭代，我定义了一个方法 iter 和 next() 来迭代shapes.List

有人可以帮助我，或者告诉我实现此功能的好方法。

谢谢

完整代码如下

---

    from string import *

    class Shape(object):
def area(self):
    raise AttributeException("Subclasses should override this method.")

def cmp(self, other):
    if type(other) != Shape and type(other) !=Square and type(other) !=Triangle and type(other) !=Circle:
        return 'Not a shape!'
    if self.area > other.area:
        return 1
    if self.area == other.area:
        return 0
    if self.area < other.area:
        return -1

    class Square(Shape):
def __init__(self, h, name):
    """
    h: length of side of the square
    """
    self.side = float(h)
    self.name = name
def area(self):
    """
    Returns area of the square
    """
    return self.side**2

def __str__(self):
    return 'Square with side ' + str(self.side)

def __eq__(self, other):
    """
    Two squares are equal if they have the same dimension.
    other: object to check for equality
    """
    return type(other) == Square and self.side == other.side

    class Circle(Shape):
def __init__(self, radius, name):
    """
    radius: radius of the circle
    """
    self.radius = float(radius)
    self.name = name

def area(self):
    """
    Returns approximate area of the circle
    """
    return 3.14159*(self.radius**2)
def __str__(self):
    return 'Circle with radius ' + str(self.radius)
def __eq__(self, other):
    """
    Two circles are equal if they have the same radius.
    other: object to check for equality
    """
    return type(other) == Circle and self.radius == other.radius

   # Problem 1: Create the Triangle class

    class Triangle(Shape):
def __init__(self, base, height, name):
    self.base= float(base)
    self.height=float(height)
    self.name = name

def area (self):
    area=float(self.base*self.height)/2
    return area

def __str__(self):
    return 'Triangle with a base ' + str(self.base) +' and height ' + str(self.height)

def __eq__ (self, other):
    return type(other)==Triangle and self.base == other.base and self.height == other.height

    #Problem 2: Create the ShapeSet class

    class ShapeSet:
def __init__(self):
    """
    Initialize any needed variables
    """
    self.List = []
    self.index=0

def addShape(self, sh):
    """
    Add shape sh to the set; no two shapes in the set may be
    identical
    sh: shape to be added
    """
    if self==[]:
        self.List.append(sh)
    else:
        for shape in self.List:
            if shape == sh:
                return 'This shape already exist'
            if shape.area == sh.area and type(shape) == type(sh):
                return 'This shape already exist'
        self.List.append(sh)

def __iter__(self):
    """
    Return an iterator that allows you to iterate over the set of
    shapes, one shape at a time
    """
    return self

def next():
    if self.index>len(self.List-1):
        StopIteration
    else:
        self.index+=1
        return self.List[self.index-1]


def __str__(self):
    """
    Return the string representation for a set, which consists of
    the string representation of each shape, categorized by type
    (circles, then squares, then triangles)
    """
    triangleList=[]
    squareList=[]
    circleList=[]
    if self.List == []:
        return 'The set is empty'
    else:
        for element in self.List:
            if type(element)==Triangle:
                triangleList.append(element.name)
            elif type(element)==Square:
                squareList.append(element.name)
            elif type(element)==Circle:
                circleList.append(element.name)
        return 'circles: %s, square: %s, triangle: %s' % (circleList, squareList, triangleList)

---

Answer 1

在你的类中，实现__cmp__而不是cmp，那么你就可以使用Python builtins，比如：

bestName = max(shapes.List)

Answer 2

您可以使用itertools module documentation 中的pairwise recipe：

from itertools import tee, izip

def pairwise(iterable):
    "s -> (s0,s1), (s1,s2), (s2, s3), ..."
    a, b = tee(iterable)
    next(b, None)
    return izip(a, b)

for previous, current in pairwise(shapes.List):
    # etc

或者你可以先找到最大面积：

max_area = max(shapes, lambda s: s.area())

然后使用它来查找该区域的所有元素：

result = [s for s in shapes if s.area() == max_area]

Answer 3

class shape():
    def __init__(self,side_length):
        self.side_length=side_length
    def area(self):
        return self.side_length*self.side_length

shape_list=[shape(i) for i in [1,6,3,12,9]]
import heapq
largest_3=heapq.nlargest(3,shape_list,key=shape.area)

for shape in largest_3:
    print shape.side_length

12
9
6