If you really want to write high-quality polished code, you have to attend to many details. A small one that is often overlooked: comments should be complete sentences. (Throughout, “comment” includes docstrings and any other English you write about your code.) Start comments with a capital, have a subject and a verb, and end them with a period.

There are a few reasons for this. First, your program should be readable. Just as you choose variable names to have meaning so that people can read your code, you should write your comments so that people can read them. Capitals are a clear indication of the start of a sentence, and a period is a clear indication of the end:

# BAD:

# try to read the thing



# BETTER:

# Try to read the thing.



Is that first comment complete? Was there meant to be a qualifying clause? The thing that what? Sure, the second sentence doesn’t explain the thing either, but at least we can see that the author didn’t just wander away in the middle of a thought.

By writing complete sentences you are more likely to include some small helper that will get your meaning across, and people will be better able to grasp what your words mean. Isn’t that why you wrote them?

The second reason to write complete sentences is to focus you on what you are writing. You think about each statement in your program, why aren’t you thinking about the comments? Maybe if you capitalize and punctuate your text, you’ll realize that a few grunted words aren’t really what you want to put there:

# EVEN BETTER:

# Try to read the configuration file, but it's OK if

# it's missing because we don't require a config file.



Some would argue that this comment is too many words, that you shouldn’t explain in that much detail, that the code should be more self-explanatory. That’s great, now you’re thinking about what the comment is doing, and making them better. I’m not suggesting writing longer comments just for bulk, if you can say it in fewer words, do, but make them good words in a complete sentence.

Paying more attention to the comments will help you write better code. I can’t tell you how many times I’ve written what I thought was a perfecty good function or line of code, then gone to write the comment or docstring, and realized a better way to do it, or even just a better name. Explaining yourself to others is a really good way to understand what you are doing. Understanding what you are doing is a really good way to write good code.

Another reason to make your comments complete sentences: it makes it easier to extend them later:

# ORIGINALLY:

# try to read the thing



# THEN SOMEONE ADDS:

# try to read the thing. Don't worry if it

# doesn't exist



The person who adds the second sentence had to add the period to the first, and now it looks really strange that the second sentence is unterminated. If the first sentence had been a real sentence, the second sentence could be added naturally.

Many coders will look at this advice and complain that it is way too nit-picking, that punctuation in comments is irrelevant, that since it’s natural language, it’s readable as it is, we don’t have to worry about trivialities like punctuation they are wrong text needs punctuation to be readable leaving it out just makes it hard to parse the sentences see what i did there?

One last reason for full sentences: the programming variant of the broken windows theory says that if you take care of small things, others are more likely to take care of the bigger things. Polished code is more likely to be maintained well and will set the tone for more polished code in the future.

And isn’t that what we all want? Write complete sentences.