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Python Python Basics (2015) Logic in Python Loop

Posted by Daniela Klimpfinger
Daniela Klimpfinger
Courses Plus Student 692 Points

Unsupported operand type(s) for +: 'NoneType' and 'str' - even though I'm working with strings only

I think this might be a bug. I have a list of strings and when looping through them I'm concatenating " World" to it. It shows me an error message that makes no sense in my opinion as it's only strings I'm working with. When I type the same code into the Python shell it works perfectly so it has to be a bug on this website.

loop.py 
hellos = [
    "Hello",
    "Tungjatjeta",
    "Grüßgott",
    "Вiтаю",
    "dobrý den",
    "hyvää päivää",
    "你好",
    "早上好"
]

for hello in hellos:
    print(hello) + " World"
Krishna Pratap Chouhan
Krishna Pratap Chouhan
15,203 Points

For python3 print is a function that takes one string argument.

The reason that it might be(didn't worked in mine though) working fine is because you are working in a Shell, try to make a file out of it and then try running it. I am sure there would be errors.

The solution is what Reyam suggested in his answer.

2 Answers

Reyam Marcos
PLUS
Reyam Marcos
Courses Plus Student 10,367 Points
Reyam Marcos
Reyam Marcos
Courses Plus Student 10,367 Points 
hellos = [
    "Hello",
    "Tungjatjeta",
    "Grüßgott",
    "Вiтаю",
    "dobrý den",
    "hyvää päivää",
    "你好",
    "早上好"
]

for hello in hellos:
    print( hello + " World")

hope it helps

Daniela Klimpfinger
Daniela Klimpfinger
Courses Plus Student 692 Points

Thank you! I didn't realize this course was in Python 3, but now it worked!

Kenneth Love
STAFF
Kenneth Love
Treehouse Guest Teacher
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

print() is a function that doesn't return a value (nothing comes out of print(), it just sends characters to the terminal. So, as far as Python is concerned, it's value is None. When you do print() + "something", Python tries to add None to "something" which it can't do.