import ctypes

#构造函数，创建了三个属性，分为用于指定初始容量，当前大小和当前数组
def __init__ (self):
        ‘Create an empty array.‘
        self._n = 0 #size
        self._capacity = 10
        self._A = self._make_array(self._capacity)

#构造函数中创建了_n属性来指定当前大小
def __len__ (self):
        return self._n

# _n指定当前大小
def is_empty(self):
        return self._n == 0

# 因为python的数组下标可以是负数，但是这边没有进行相应的实现，有兴趣的可以自行实现
def __getitem__ (self, k):
        if not 0  self._n:
            raise ValueError(‘invalid index‘) 
        return self._A[k]

def append(self, obj):
        #当数组当前元素已满时，扩充容量为原来的两倍，在进行追加
        if self._n == self._capacity:
            self._resize(2 * self._capacity)
        self._A[self._n] = obj    
        self._n += 1

def _make_array(self, c):
        return (c * ctypes.py_object)( )
    
    def _resize(self, c):
        B = self._make_array(c)
        #扩充之后，需要将原数组中的元素copy到新数组中
        for k in range(self._n):
            B[k] = self._A[k]
        self._A = B
        self._capacity = c

def insert(self, k, value):
        #当数组当前元素已满时，扩充容量为原来的两倍，在进行insert
        if self._n == self._capacity:
            self._resize(2 * self._capacity)
        for j in range(self._n, k, -1):
            self._A[j] = self._A[j-1]
        self._A[k] = value
        self._n += 1

def pop(self,idx):
        if idx >= self._n:
            raise ValueError( ‘index out of bounds‘ )
        for i in range(idx,self._n - 1):
            self._A[i]=self._A[i+1]
        self._A[self._n - 1] = None
        self._n -= 1

def remove(self, value):
        for k in range(self._n):
            if self._A[k] == value:
                for j in range(k, self._n - 1):
                    self._A[j] = self._A[j+1]
                self._A[self._n - 1] = None
                self._n -= 1
                return
        raise ValueError( ‘value not found‘ )

def _print(self):
        for i in range(self._n):
            print(self._A[i], end = ‘ ‘)
        print()

mylist = DynamicArray()
print (‘size was: ‘, str(len(mylist)))
mylist.append(10)
mylist.append(20)
mylist.append(30)
mylist.insert(0, 0)
mylist.insert(1, 5)
mylist.insert(3, 15)
mylist._print()
mylist.remove(20)
mylist._print()

print (‘size is: ‘, str(len(mylist)))
mylist.pop(3)
mylist._print()
print (‘size is: ‘, str(len(mylist)))