Hashes without Hash, integer edition

2022-03-07.py

import os.path
from os import path
import csv

question = """

Implement a hashmap from scratch without any existing libraries in your preferred language.

A hashmap should:

Be empty when initialized
Have the function put(int key, int value) which inserts a (key, value) pair into the hashmap. 
If the key already exists, update the corresponding value.
Have the function get(int key) which returns the value to which the specified key is mapped, or -1 if there's no mapping for the key.
Have the function remove(key) which removes the key and its value if it exists in the map.

"""

hashmap_file = './hashmap.csv'

def put(input_key, input_value):
    new_data = []
    input_key = str(input_key)
    new_line = [input_key, input_value]
    updated = False
    if path.exists(hashmap_file):
        with open(hashmap_file, newline='') as hashmap:
            reader = csv.reader(hashmap)
            for key_value in reader:
                if input_key == key_value[0]:
                    new_data.append(new_line)
                    updated = True
                else:
                    new_data.append(key_value)
    if updated == False:
        new_data.append(new_line)
    with open(hashmap_file, 'w', newline='') as hashmap:
        writer = csv.writer(hashmap)
        writer.writerows(new_data)
    return
    
def get(input_key):
    input_key = str(input_key)
    if path.exists(hashmap_file):
        with open(hashmap_file, newline='') as hashmap:
            reader = csv.reader(hashmap)
            for key_value in reader:
                if input_key == key_value[0]:
                    return key_value[1]
    return -1

def remove(input_key):
    input_key = str(input_key)
    new_data = []
    deleted = False
    if path.exists(hashmap_file):
        with open(hashmap_file, newline='') as hashmap:
            reader = csv.reader(hashmap)
            for key_value in reader:
                if input_key == key_value[0]:
                    deleted = True
                else:
                    new_data.append(key_value)
    with open(hashmap_file, 'w', newline='') as hashmap:
        writer = csv.writer(hashmap)
        writer.writerows(new_data)
    return

# populate hash

put(1, '1')
put(2, '2')
put(3,'3')

# test get

print(get(1))

# test put: new value
put(4, '4')
print(get(4))

# test put: updating existing value
put(4, 'cuatro')
print(get(4))

# test remove
remove(3)
print(get(3))