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Comments in Python are quite simple. Let's take a look.

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We'll start by making a working copy of comments.py,

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and we'll call it comments-working.py.

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We'll go ahead and open the working copy.

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And here we have a little program that generates a list of prime numbers.

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Now, you'll notice that at the top of the file, we have a number of lines that

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are introduced by a Pound sign.

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I call it a Pound sign some people called the Hash Mark, or that tick-tack-toe-

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looking thingie, whatever we call it.

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That is the symbol that indicates a comment in Python.

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So everything starting with the Pound sign, and all the way to the end of the

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line, is ignored by the Python interpreter.

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So all these are comments.

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You'll notice that we don't have any comments in the rest of the code.

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And this is a piece of code that may very well benefit from some comments.

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So for example, this line here, I might have a comment that says # generate a

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list of prime numbers.

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And now when somebody comes back and looks at the code later on he'll, see this:

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for n in primes generate a list of prime numbers.

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Oh, well I guess that's what that does.

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Now, when you're reading comments you want to be careful that you don't just

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trust the comment, that you actually look at the code and make sure that the

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code actually does what you think it does.

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Use the comment as a guideline, but oftentimes as people are writing code they

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might put in a comment and then maybe change the code later, forget to change

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the comment, or perhaps their terminology is a little bit different than what you're expecting.

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So comments are very useful.

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The purpose of comments is to make the code more readable by human beings,

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because something like this here, I wrote it, so I know what it does, but you're

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looking at it and you might say, hmm, what algorithm is he using to generate

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these prime numbers?

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And so a couple of little comments might make it a lot more readable. For example,

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I can say # one is never prime by definition.

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And over here I might say # found a divisor, not prime.

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And over here, because we have a generator function and a lot of people who

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aren't familiar with Python might not know what a generator function is,

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I can say, # yield makes this a generator.

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And it'll at least give somebody a clue. They can look that up if they don't

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know what that means.

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So the principle here is to use comments to make the code a little bit more clear.

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There is a danger, of course, if you use too many comments, if you comment every

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line, or if you comment way too many things.

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The comments might become a distraction.

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But just keep in mind that the purpose of the comment is to make the code more

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clear to somebody who is reading it for the first time and may not be familiar

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with the algorithm that you are using.

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So comments in Python are introduced by a Pound sign or Hash Mark.

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And everything from that Pound sign to the end of the line is ignored by the

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interpreter, and therefore considered a comment.