Implementation.py

#Although arrays are pre-defined in Python in the form of lists, we can implement our own arrays.
#Here, we will implement our own array with some common methods such as access, push, pop, insert, delete

class MyArray():
    def __init__(self):
        self.length = 0 #We initialize the array's length to be zero
        self.data = {} #We initialize the data of the array using an empty dictionary. The keys will correspond to the index and the values to the data

    #The attributes of the array class are stored in a dictionary by default.
    #When the __dict__ method is called on an instance of the class it returns the attributes of the class along with their values in a dictionary format
    #Now, when the instance of the class is printed, it returns a class object with its location in memory.
    #But we know when we print the array we get the elements of the array as output
    #When we print the instance of the class, the built-in __str__ method is called. So we can modify the __str__ method inside the class
    #To suit our needs.
    def __str__(self):
       return str(self.__dict__) #This will print the attributes of the array class(length and dsata) in string format when print(array_instance) is executed

    def get(self, index):
        return self.data[index] #This method takes in the index of the element as a parameter and returns the corresponding element in O(1) time.

    def push(self, item):
        self.length += 1
        self.data[self.length - 1] = item #Adds the item provided to the end of the array

    def pop(self):
        last_item = self.data[self.length-1] #Collects the last element
        del self.data[self.length - 1] #Deletes the last element from the array
        self.length -= 1 #Decrements the length attribute of the array by 1
        return last_item #Returns the popped element. O(1) time

    def insert(self, index, item):
        self.length += 1
        for i in range(self.length-1, index, -1):
            self.data[i] = self.data[i-1] #Shifts every element from the index to the end by one place towards right. Thus making space at the specified index
        self.data[index] = item #Adds the element at the given index. O(n) operation


    def delete(self,index):
        for i in range(index, self.length-1):
            self.data[i] = self.data[i+1] #Shifts elements from the given index to the end by one place towards left
        del self.data[self.length - 1] #The last element which remains two times in the array is deleted
        self.length -= 1 #The lenght is decremented by 1. O(n) operation



arr = MyArray()
arr.push(6)
#{'length': 1, 'data': {0: 6}}

arr.push(2)
#{'length': 2, 'data': {0: 6, 1: 2}}

arr.push(9)
#{'length': 3, 'data': {0: 6, 1: 2, 2: 9}}

arr.pop()
#{'length': 2, 'data': {0: 6, 1: 2}}

arr.push(45)
arr.push(12)
arr.push(67)
#{'length': 5, 'data': {0: 6, 1: 2, 2: 45, 3: 12, 4: 67}}

arr.insert(3,10)
#{'length': 6, 'data': {0: 6, 1: 2, 2: 45, 3: 10, 4: 12, 5: 67}}

arr.delete(4)
#{'length': 5, 'data': {0: 6, 1: 2, 2: 45, 3: 10, 4: 67}}

print(arr.get(1))
#2

print(arr)
#The outputs given after each function call are the outputs obtained by calling print(arr) and not by the function calls themselves