dynamic_arrays.py

import ctypes


# Dynamic Array
class DynamicArrays(object):
    def __init__(self):
        self.n = 0
        self.capacity = 1
        self.A = self.make_array(self.capacity)

    def __len__(self):
        return self.n

    def __getitem__(self):
        if not 0 <= k < self.n:
            return IndexError('k is out of bounds')
        return self.A[k]

    def append(self, elem):
        if self.n == self.capacity:
            self._resize(2*self.capacity) # 2x if capacity isn't enough
        self.A[self.n] = elem
        self.n += 1

    def _resize(self, capacity):
        B = self.make_array(capacity)

        for i in range(self.n):
            B[i] = self.A[i]

        self.A = B
        self.capacity = capacity

    def make_array(self, capacity):
        return (capacity*ctypes.py_object)()



arr = DynamicArrays()
arr.append(20)
arr.append(30)
len(arr)