CS102 - Hash Maps - Blossom Project

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#1

https://www.codecademy.com/paths/computer-science/tracks/cspath-cs-102/modules/hash-maps/projects/blossom
Hello, I am newbie, first time leaner here. I have questions for this exercise and hope they’re not too silly.

This is the final code:

from linked_list import Node, LinkedList
class HashMap:
  def __init__(self,size):
    self.array_size = size
    self.array = [LinkedList() for i in range(size)]
  def hash(self,key):
    hash_code = sum(key.encode())
    return hash_code
  def compress(self,hash_code):
    return hash_code % self.array_size

  def assign(self,key,value):
    array_index = self.compress(self.hash(key))
    payload = Node([key,value])
    list_at_array = self.array[array_index]
    for item in list_at_array:
      if key == item[0]:
        item[1] = value
        return
    list_at_array.insert(payload)       

  def retrieve(self,key):
    array_index = self.compress(self.hash(key))
    list_at_index = self.array[array_index]
    for item in list_at_index:
      if item[0] == key:
        return item[1]
      else:
        return None

So first, since each index of the array is a Linked List, how is it possible to iterate through the Linked List by this?

    list_at_array = self.array[array_index]
    for item in list_at_array:

And secondly, why don’t we insert the new [key,value] directly to self.array[array_index] but instead insert them through an instance variable list_at_array. Doesn’t it only assign the new [key,value] to the instance variable, and not the array index it self?
I mean the code works perfectly fine. But I just don’t get it.

  def assign(self,key,value):
    array_index = self.compress(self.hash(key))
    payload = Node([key,value])
    list_at_array = self.array[array_index]
    for item in list_at_array:
      if key == item[0]:
        item[1] = value
        return
    list_at_array.insert(payload)

So much thanks in advance.

#2

I don’t remember if they talked about this when teaching LinkedList, but there’s code in linked_list.py that allows iteration through the list. The folder icon lets you open the other files available for the lesson.

  def __iter__(self):
    current_node = self.head_node
    while(current_node):
      yield current_node.get_value()
      current_node = current_node.get_next_node()

I think it’s using the variable to make it easier to follow, this seems to work:

  def assign(self, key, value):
    array_index = self.compress(self.hash(key))
    payload = Node([key, value])
    #list_at_array = self.array[array_index]
    for i in self.array[array_index]:
      if key == i[0]:
        i[1] = value
        return
    self.array[array_index].insert(payload)
#3

Thanks a lot @bavarcarus .
It makes more sense now with the iter method.
And this one also seems to be better to understand to me:

  def assign(self, key, value):
    array_index = self.compress(self.hash(key))
    payload = Node([key, value])
    #list_at_array = self.array[array_index]
    for i in self.array[array_index]:
      if key == i[0]:
        i[1] = value
        return
    self.array[array_index].insert(payload)

But I just don’t get why the original one I posted still works… :joy:

#4

The original that you posted is just assigning a new name to the same object.
if you had a variable that was named this_is_way_too_long_but_I_cannot_change_it
you could just say stupid_name = this_is_way_too_long_but_I_cannot_change_it