类__init__()需要2个参数（给了1个）

Question

我正在学习Python中的类。运行了两个例子，这两个例子里的函数都有两个参数（其中一个是给定的），但是只有一个例子能执行，另一个却不能。

这个例子能执行，尽管x.setdata()只有一个参数。 class FirstClass: def setdata(self,value): self.data=value def display(self): print(self.data)

#make two instances
x=FirstClass()
y=FirstClass()

x.setdata("king arthur") #call methods: self is x?? 
y.setdata(3.31212)

x.display()
y.display()

这个例子却无法运行，错误信息是msg: __init__() takes exactly 2 arguments (1 given)：

class Heap:

        def __init__(self, sorting_key):
            """Initializes a new instance of a heap.

            Args:
                sorting_key: Specifies the attribute of the object inserted
                into the heap, on the basis of which the heap was created.
            """
            self.heap = list()
            self.mapping = dict()
            self.sorting_key = sorting_key

        def heapify_up(self, child):
                """Standard heapify operation, as described in CLRS.
                Works by swapping the element originially at index child in the heap
                with its parent until the heap property is satisfied. Modifies the
                appropriate heap attribute

                Args:
                    child: Index of the element that violates the heap property

                Returns:
                    None
                """
                parent = (child - 1) / 2
                # Swaps the element originally at the index child with its parent
                # until the value of the specifed attribute of the parent is greater
                # than the value of the specified attribute of the element itself
                while (getattr(self.heap[parent], self.sorting_key) <
                       getattr(self.heap[child], self.sorting_key)):
                    if (parent == -1):
                        # This means child was 0, which means we have reached the
                        # top of the heap
                        return

                    # Swap the mappings as well to ensure that future references in
                    # the mapping dict refer to the correct position of the object in
                    # the heap
                    self.mapping[self.heap[parent].player] = child
                    self.mapping[self.heap[child].player] = parent

                    # Swap the parent and the child
                    temp = self.heap[parent]
                    self.heap[parent] = self.heap[child]
                    self.heap[child] = temp

                    # Move the child and parent pointers up the heap
                    child = parent
                    parent = (child - 1) / 2


    x=Heap()
    x.__init__([42,32,54,1,3])

    x.heapify_up(l,5)
    print x

Answer 1

这两行：

x=Heap()
x.__init__([42,32,54,1,3])

应该合并成一行：

x=Heap([42,32,54,1,3])

记住，当你执行 Heap() 时，Heap.__init__ 会自动被调用。下面是一个演示：

>>> class Foo:
...     def __init__(self):
...         print("Foo.__init__ was called")
...
>>> Foo()
Foo.__init__ was called
<__main__.Foo object at 0x020AF030>
>>>