Arrays.py

import ctypes # provides low-level arrays

class DynamicArray:
    """A dynamic array class akin to a simplified Python list."""

    def __init__ (self):
        """Create an empty array."""
        self._n = 0 # count actual elements
        self._capacity = 1 # default array capacity
        self._A = self._make_array(self._capacity) # low-level array

    def __len__ (self):
        """Return number of elements stored in the array."""
        return self._n

    def __getitem__ (self, k):
        """Return element at index k."""
        if not 0 <= k < self._n:
            raise IndexError('invalid index' )
        return self._A[k]

    def append(self, obj):
        """Add object to end of the array."""
        if self._n == self._capacity:          # not enough room
            self._resize(2*self._capacity)
        self._A[self._n] = obj
        self._n += 1

    def insert(self, obj, index):
        """Add object to the specified index of the array."""
        if self._n == self._capacity : # not enough room
            self._resize(2*self._capacity) # so double capacity
        if index > self._n:
            raise IndexError('invalid index')
        for i in range(self._n, index, -1):
            self._A[i] = self._A[i-1]
        self._A[index] = obj
        self._n += 1

    def delete(self, index):
        """Delete object from the specified index of the array."""
        if (index >= self._n) or (index < 0):
            raise IndexError('invalid index')
        for i in range(index, self._n - 1):
            self._A[i] = self._A[i+1]
        self._n -= 1

    def _resize(self, c): # nonpublic utitity
        """Resize internal array to capacity c."""
        B = self._make_array(c) # new (bigger) array
        for k in range(self._n): # for each existing value
            B[k] = self._A[k]
        self._A = B # use the bigger array
        self._capacity = c

    def _make_array(self, c): # nonpublic utitity
        """Return new array with capacity c."""
        return (c*ctypes.py_object)()

    def print_array_details(self):
        "Prints array, capacity and length"
        print("------------------------------------------")
        print("Length of array is "+ str(self._n))
        print("Capacity of array is " + str(self._capacity))
        print("Array is " )
        for i in range(self._n):
            print(str(self._A[i]) + " ")

A = DynamicArray()
A.print_array_details()
A.insert(2,0)
A.print_array_details()
A.delete(0)
A.print_array_details()
A.append(5)
A.append(15)
A.print_array_details()