 There are three types of errors that you can make in Python. The first type is called a syntax error. By the way, this number sign that I'm typing in the shell is a comment. That means Python should ignore it. It's just there for us humans to read. A syntax error happens when you say some of this grammatically incorrect in Python. So for example, if I try to say 34 plus times 8, that doesn't make any sense. Mathematically, it's just wrong on every possible level. So when I press the Enter key, the shell will respond, showing me the star is where it got confused and says that's invalid syntax. You can have another kind of error called a runtime error. This happens when you do something that is syntactically valid. It's grammatically valid. For example, if I try to evaluate 42 divided by 0. Well, syntactically in terms of grammar, I have two numbers and a division sign between them. But when it comes time to actually run that calculation, I get an error that says zero division error because you can't divide by zero. These two types of errors are usually pretty easy to find. Syntax error is the easiest because the compiler points them right out to you and runtime errors because once you run the program, you see the error front and center. The third type of error is called the semantic error, which means you said something that's syntactically correct grammatically, and it's not going to cause any errors when you run the program, but it doesn't do what you wanted it to. So for example, if I wanted to find out how many days there are approximately in 25 years, and I accidentally type 25 plus 365, there's nothing wrong with that in terms of mathematics. I have two numbers with the plus sign. There's no runtime error because I can certainly add 25 and 365, but the number I get is nowhere near the correct answer because I've said something that is a semantic error. I didn't do the computation I intended to do. Semantic errors in general are the hardest ones to find because the compiler can't help you, the runtime system can't help you. It's only when you as a human look at the result and say, wow, this is not what I intended.