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Commenting code

From: Python 3 Essential Training

Video: Commenting code

Comments in Python are quite simple. Let's take a look. We'll start by making a working copy of comments.py, and we'll call it comments-working.py. We'll go ahead and open the working copy. And here we have a little program that generates a list of prime numbers. Now, you'll notice that at the top of the file, we have a number of lines that are introduced by a Pound sign. I call it a Pound sign some people called the Hash Mark, or that tick-tack-toe- looking thingie, whatever we call it.

Commenting code

Comments in Python are quite simple. Let's take a look. We'll start by making a working copy of comments.py, and we'll call it comments-working.py. We'll go ahead and open the working copy. And here we have a little program that generates a list of prime numbers. Now, you'll notice that at the top of the file, we have a number of lines that are introduced by a Pound sign. I call it a Pound sign some people called the Hash Mark, or that tick-tack-toe- looking thingie, whatever we call it.

That is the symbol that indicates a comment in Python. So everything starting with the Pound sign, and all the way to the end of the line, is ignored by the Python interpreter. So all these are comments. You'll notice that we don't have any comments in the rest of the code. And this is a piece of code that may very well benefit from some comments. So for example, this line here, I might have a comment that says # generate a list of prime numbers.

And now when somebody comes back and looks at the code later on he'll, see this: for n in primes generate a list of prime numbers. Oh, well I guess that's what that does. Now, when you're reading comments you want to be careful that you don't just trust the comment, that you actually look at the code and make sure that the code actually does what you think it does. Use the comment as a guideline, but oftentimes as people are writing code they might put in a comment and then maybe change the code later, forget to change the comment, or perhaps their terminology is a little bit different than what you're expecting.

So comments are very useful. The purpose of comments is to make the code more readable by human beings, because something like this here, I wrote it, so I know what it does, but you're looking at it and you might say, hmm, what algorithm is he using to generate these prime numbers? And so a couple of little comments might make it a lot more readable. For example, I can say # one is never prime by definition. And over here I might say # found a divisor, not prime.

And over here, because we have a generator function and a lot of people who aren't familiar with Python might not know what a generator function is, I can say, # yield makes this a generator. And it'll at least give somebody a clue. They can look that up if they don't know what that means. So the principle here is to use comments to make the code a little bit more clear. There is a danger, of course, if you use too many comments, if you comment every line, or if you comment way too many things.

The comments might become a distraction. But just keep in mind that the purpose of the comment is to make the code more clear to somebody who is reading it for the first time and may not be familiar with the algorithm that you are using. So comments in Python are introduced by a Pound sign or Hash Mark. And everything from that Pound sign to the end of the line is ignored by the interpreter, and therefore considered a comment.

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This video is part of

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Python 3 Essential Training

87 video lessons · 37653 viewers

Bill Weinman
Author

 
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  1. 5m 14s
    1. Welcome
      1m 32s
    2. Understanding prerequisites for Python
      2m 4s
    3. Using the exercise files
      1m 38s
  2. 33m 29s
    1. Getting started with "Hello World"
      4m 43s
    2. Selecting code with conditionals
      4m 45s
    3. Repeating code with a loop
      4m 13s
    4. Reusing code with a function
      2m 43s
    5. Creating sequences with generator functions
      2m 46s
    6. Reusing code and data with a class
      4m 39s
    7. Greater reusability with inheritance and polymorphism
      7m 17s
    8. Handling errors with exceptions
      2m 23s
  3. 22m 32s
    1. Installing Python 3 and Eclipse for Windows
      11m 24s
    2. Installing Python 3 and Eclipse for Mac
      11m 8s
  4. 28m 0s
    1. Creating a main script
      3m 27s
    2. Understanding whitespace in Python
      4m 8s
    3. Commenting code
      3m 28s
    4. Assigning values
      3m 37s
    5. Selecting code and values with conditionals
      4m 46s
    6. Creating and using functions
      3m 54s
    7. Creating and using objects
      4m 40s
  5. 31m 23s
    1. Understanding variables and objects in Python
      2m 46s
    2. Distinguishing mutable and immutable objects
      2m 41s
    3. Using numbers
      3m 34s
    4. Using strings
      6m 38s
    5. Aggregating values with lists and tuples
      4m 55s
    6. Creating associative lists with dictionaries
      4m 24s
    7. Finding the type and identity of a variable
      4m 45s
    8. Specifying logical values with True and False
      1m 40s
  6. 9m 42s
    1. Selecting code with if and else conditional statements
      2m 22s
    2. Setting multiple choices with elif
      2m 14s
    3. Understanding other strategies for multiple choices
      2m 38s
    4. Using the conditional expression
      2m 28s
  7. 11m 26s
    1. Creating loops with while
      1m 27s
    2. Iterating with for
      3m 54s
    3. Enumerating iterators
      3m 22s
    4. Controlling loop flow with break, continue, and else
      2m 43s
  8. 23m 28s
    1. Performing simple arithmetic
      2m 14s
    2. Operating on bitwise values
      3m 30s
    3. Comparing values
      3m 32s
    4. Operating on Boolean values
      2m 59s
    5. Operating on parts of a container with the slice operator
      6m 52s
    6. Understanding operator precedence
      4m 21s
  9. 11m 34s
    1. Using the re module
      1m 4s
    2. Searching with regular expressions
      3m 12s
    3. Replacing with regular expressions
      3m 29s
    4. Reusing regular expressions with re.compile
      3m 49s
  10. 9m 10s
    1. Learning how exceptions work
      1m 18s
    2. Handling exceptions
      4m 15s
    3. Raising exceptions
      3m 37s
  11. 23m 1s
    1. Defining functions
      6m 23s
    2. Using lists of arguments
      2m 26s
    3. Using named function arguments
      4m 32s
    4. Returning values from functions
      1m 55s
    5. Creating a sequence with a generator function
      7m 45s
  12. 47m 29s
    1. Understanding classes and objects
      5m 12s
    2. Using methods
      6m 12s
    3. Using object data
      10m 4s
    4. Understanding inheritance
      5m 11s
    5. Applying polymorphism to classes
      7m 13s
    6. Using generators
      9m 48s
    7. Using decorators
      3m 49s
  13. 18m 54s
    1. Understanding strings as objects
      3m 25s
    2. Working with common string methods
      5m 24s
    3. Formatting strings with str.format
      5m 31s
    4. Splitting and joining strings
      2m 49s
    5. Finding and using standard string methods
      1m 45s
  14. 25m 27s
    1. Creating sequences with tuples and lists
      4m 6s
    2. Operating on sequences with built-in methods
      5m 50s
    3. Organizing data with dictionaries
      4m 56s
    4. Operating on character data with bytes and byte arrays
      10m 35s
  15. 11m 46s
    1. Opening files
      2m 4s
    2. Reading and writing text files
      4m 33s
    3. Reading and writing binary files
      5m 9s
  16. 21m 27s
    1. Creating a database with SQLite 3
      6m 56s
    2. Creating, retrieving, updating, and deleting records
      7m 31s
    3. Creating a database object
      7m 0s
  17. 18m 27s
    1. Using standard library modules
      8m 0s
    2. Finding third-party modules
      5m 47s
    3. Creating a module
      4m 40s
  18. 23m 11s
    1. Dealing with syntax errors
      8m 19s
    2. Dealing with runtime errors
      4m 0s
    3. Dealing with logical errors
      4m 22s
    4. Using unit tests
      6m 30s
  19. 19m 56s
    1. Normalizing a database interface
      6m 39s
    2. Deconstructing a database application
      8m 9s
    3. Displaying random entries from a database
      5m 8s
  20. 29s
    1. Goodbye
      29s

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