7. Comments¶

As programs get bigger and more complicated, they get more difficult to read. Formal languages are dense, and it is often difficult to look at a piece of code and figure out what it is doing, or why. For this reason, it is a good idea to add notes to your programs to explain in natural language what the program is doing. These notes are called comments.

A comment in a computer program is text that is intended only for the human reader - it is completely ignored by the interpreter. In Python, the # token starts a comment. The rest of the line is ignored. Here is a new version of Hello, World!.

#--------------------------------------------------- # This demo program shows off how elegant Python is! # Written by Joe Soap, December 2010. # Anyone may freely copy or modify this program. #--------------------------------------------------- print("Hello, World!") # Isn't this easy!

Notice that when you run this program, it still only prints the phrase Hello, World! None of the comments appear. You’ll also notice that we’ve left a blank line in the program. Blank lines are also ignored by the interpreter, but comments and blank lines can make your programs much easier for humans to parse. Use them liberally!

Check your understanding

What are comments for?
• To tell the computer what you mean in your program.
• Comments are ignored by the computer.
• For the people who are reading your code to know, in natural language, what the program is doing.
• The computer ignores comments. It’s for the humans that will “consume” your program.
• Nothing, they are extraneous information that is not needed.
• Comments can provide much needed information for anyone reading the program.
• Nothing in a short program. They are only needed for really large programs.
• Even small programs benefit from comments.