can only concatenate str (not "list") to str

This error occurs when you try to concatenate a list to a string using the + operator. In Python, you can only concatenate strings with other strings, not with lists.

For example, if you have a string variable 'name' and a list variable 'numbers', and you try to concatenate them like this:

name = "John"
numbers = [1, 2, 3]
result = name + numbers

You will get the error message:

TypeError: can only concatenate str (not "list") to str

To fix this error, you need to convert the list to a string before concatenating it with the string. You can do this using the join() method:

name = "John"
numbers = [1, 2, 3]
result = name + ", ".join(str(n) for n in numbers)

This will convert each number in the list to a string and join them with a comma and space, resulting in a new string that can be concatenated with the original string.