How to modify a key value from a user inputs request

I am making a basic app where I let the user add, delete and edit the stock they have. I am trying to make it so I can let the user either ‘add’ or ‘remove’ which they decide and type it and the input captures their response. I don’t to use a load of if user_input = ‘add’ do this and then elif user_input == ‘remove’ do that. What would be the best way to go around this.

Here is my code for the edit inventory part;

    def edit_inventory(self):
        item_name = input('Enter item name: ')

        try:
            user_input = input('Type \'ADD\' or \'REMOVE\' to change quantity: ').lower()
            if user_input not in ['add', 'remove']:
                raise ValueError
            quantity = int(input(f'Enter how many you wish to {user_input}: '))
            if user_input == 'add':
                for item_name in self.stock.keys():
                    self.stock[item_name] += quantity
            elif user_input == 'remove':
                for item_name in self.stock.keys():
                    self.stock[item_name] -= quantity

        except KeyError:
            print('Item not in stock. Check current stock for current inventory.')
        except ValueError:
            print('Invalid response.')

I want to work around the if and elif to make it more efficient.

>Solution :

One approach is to use a dispatch table, like this:

def add_item(self, item):
    # code to add an item

def remove_item(self, item):
    # code to remove an item

def edit_inventory(self):
    cmd_table = {
        'add': self.add_item,
        'remove': self.remove_item,
    }
    item_name = input('Enter item name: ')
    cmd = input("Type 'ADD' or 'REMOVE' to change quantity: ").lower()
    cmd_func = cmd_table[cmd]  # raises KeyError automatically if cmd is invalid
    # add whatever other stuff, e.g. getting quantity
    cmd_func(item)

This way if you have a large number of commands, you just need one entry in the dictionary per command, rather than a bunch of if/elif. You also get reasonable behavior around invalid entries for free; you can use [] and get a KeyError, or you can use .get() and supply a default function, or you can test if cmd in cmd_table.