hash_table.py

class HashTable:
    """
    The HashTable class
    """
    def __init__(self) -> None:
        self.collection = {}
    
    def hash(self, string: str) -> int:
        # This function calculates the hash value of a given string
        # by summing the ASCII values of its characters.
        hash_list = [ord(char) for char in string]
        return sum(hash_list)

    def add(self, key: str, value: str) -> None:
        # This function adds a key-value pair to the hash table.
        hash_val = self.hash(key)
        if hash_val in self.collection:
            self.collection[hash_val][key] = value
            return
        self.collection[hash_val] = {key: value}

    def remove(self, key: str) -> None:
        # This function removes a key-value pair from the hash table.
        hash_val = self.hash(key)
        if hash_val in self.collection and key in self.collection[hash_val]:
            del self.collection[hash_val][key]

    def lookup(self, key: str):
        # This function looks up a value in the hash table by its key.
        hash_val = self.hash(key)
        if hash_val in self.collection and key in self.collection[hash_val]:
            return self.collection[hash_val][key]
        return None
    
    def __str__(self):
        # This function returns a string representation of the hash table.
        return str(self.collection)
        
def end_program_statement():
    # This function is called when the user wants to exit the program.
    print("\nExiting the program.")
    exit()

def menu():
    # This function is called when the user wants to see the menu again.
    print(
    '\nFind hash value of a string ⇾ 1\n'+
    'Add key-value pair to collection ⇾ 2\n'+
    'Remove key-value pair ⇾ 3\n'+
    'Lookup value in collection by key ⇾ 4\n'
    'View collection ⇾ 5\n'+
    'Type "q", "quit", "exit" or Ctrl+C to exit the program.'
    )

def menu_reminder():
    print('Type 6 to see the menu again.')


# The program starts here.
print('<<< HASH TABLE >>>\n')
print(
'This is a simple implementation of a hash table in Python.\n'+
'The hash table uses a simple hash function that sums the ASCII values of the characters in the key.\n'+
'The hash table uses chaining to handle collisions.\n'+
'The hash table supports adding, removing, and looking up key-value pairs.\n')

hash_table = HashTable()
menu()

while True:
    try:
        inp = input("\nEnter your choice (1-6): ").strip()
    except KeyboardInterrupt:
        end_program_statement()

    if inp.lower() in ['q', 'quit', 'exit']:
        end_program_statement()

    if inp == '1':
        string = input("Enter a string to find its hash value: ").strip()
        print(f"The hash value of '{string}' is: {hash_table.hash(string)}")
        menu_reminder()
    elif inp == '2':
        key = input("Enter a key: ").strip()
        value = input("Enter a value: ").strip()
        hash_table.add(key, value)
        print(f"Added key-value pair: {key}: {value}")
        menu_reminder()
    elif inp == '3':
        key = input("Enter a key to remove: ").strip()
        hash_table.remove(key)
        print(f"Removed key: {key}")
        menu_reminder()
    elif inp == '4':
        key = input("Enter a key to lookup: ").strip()
        value = hash_table.lookup(key)
        if value is not None:
            print(f"The value for key '{key}' is: {value}")
        else:
            print(f"Key '{key}' not found.")
        menu_reminder()
    elif inp == '5':
        print(f"Collection: {hash_table}")
        menu_reminder()
    elif inp == '6':
        menu()
    else:
        print("Invalid choice. Please try again.")
        menu_reminder()