Why won't the user inputed value add to the created dictionary in the while loop in python?

I tried creating a while loop that prompts the user to input the abbreviation for the state and if it is not already included in the dictionary to add it to the dictionary with the capital of the state. I have been having an issue where it won't add the abbreviation into the dictionary correctly and need some help trying to fix it. Thanks.
This is the code I used:

states = {'ID': 'Boise', 'VT': 'Montpelier', 'SD': 'Pierre', 'ND': 'Bismark'}
length = len(states)
add_state = input('Enter state abrev. or Enter to quit ')
while add_state != '':
    if add_state in states:
        print(f'Already have {add_state}, capital', states[add_state])
        add_state = input('Enter state abrev. or Enter to quit ')
    else:
        capital = input(f'Enter capital of {add_state} ')
        add_state = input('Enter state abrev. or Enter to quit ')
        states[add_state] = capital
print(states)

This is a sample output that I would get after:

Enter state abrev. or Enter to quit CA
Enter capital of CA sacremento
Enter state abrev. or Enter to quit 
{'ID': 'Boise', 'VT': 'Montpelier', 'SD': 'Pierre', 'ND': 'Bismark', '': 'sacremento'}

The CA was not included when inputting the values into the dictionary.

The reason the state "CA" wasn't included in the list is because when you you reassigned the add_state variable in the line add_state = input('Enter state abrev. or Enter to quit ') in the else: block. In this case it was assigned to an empty string ("") when you hit enter. Then the string "sacramento" was was saved under an empty string.

Try reformatting your code by including the input prompt inside the while loop and removing the other prompts (except the one outside the while loop):

states = {'ID': 'Boise', 'VT': 'Montpelier', 'SD': 'Pierre', 'ND': 'Bismark'}
length = len(states)
add_state = input('Enter state abrev. or Enter to quit ')
while add_state != '':
    if add_state in states:
        print(f'Already have {add_state}, capital', states[add_state])
    else:
        capital = input(f'Enter capital of {add_state} ')
        states[add_state] = capital
    # Moved input prompt here:
    add_state = input('Enter state abrev. or Enter to quit ')
print(states)

Output:

Enter state abrev. or Enter to quit CA
Enter capital of CA sacramento
Enter state abrev. or Enter to quit 
{'ID': 'Boise', 'VT': 'Montpelier', 'SD': 'Pierre', 'ND': 'Bismark', 'CA': 'sacramento'}