I get this error when i run this code “TypeError: can only concatenate str (not ”NoneType“) to str”, why?

Question

I tried running this code and it gave me this error, "TypeError: can only concatenate str (not "NoneType") to str". I need to know what to do.

I tried using '' or "True" instead of "None"

users = {'zacc_eli':{'first_name': 'Zaccheus',
                     'middle_name': None,
                     'last_name': 'Elisha',
                     'age': 19},
         '_Djvy_': {'first_name': 'daniel',
                    'middle_name': 'joshua',
                    'last_name': 'adebayo',
                    'age': None}}

for username, details in users.items():
    print(username + ':')
    full_name = details['first_name'] + ' ' + details['middle_name'] + ' ' + details['last_name']
    full_name2 = details['first_name'] + ' ' + details['last_name']
    age = details['age']

    if details['middle_name'] == None :
        print('\tFull Name: ' + full_name2.title())
    else:
        print('\tFull Name: ' + full_name.title())

    if details['age'] != None:
        print('\tAge: ' + str(age))

I expect no double space when there is no middle name and no age when there is no age.

Answer 1

This line

full_name = details['first_name'] + ' ' + details['middle_name'] + ' ' + details['last_name']

fails if details['middle_name'] is None rather than a str value. At this point, though, you haven't checked if that is the case. You don't do that until 4 lines later.

Python is not lazy (like Haskell); it doesn't wait until you actually use the value of full_name to evaluate the expression assigned to it.

Instead, check the value before you do anything that requires a str :

for username, details in users.items():
    print(username + ':')
    first = details['first_name']
    middle = details['middle_name']
    last = details['last_name']
    if middle is None:
        full_name = first + ' ' + last
    else:
        full_name = first + ' ' + middle + ' ' + last

    # Or a one-liner
    # full_name = ' '.join([for x in [first, middle, last] if x is not None])
    age = details['age']

    print('\tFull Name: ' + full_name.title())

    if age is not None:
        print('\tAge: ' + str(age))