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Displaying random entries from a database

From: Python 3 Essential Training

Video: Displaying random entries from a database

Here we have a simple database application that displays a list of random testimonials or quotes on a web page. If you look at my web page, I actually used this for testimonials. And every time the page gets reloaded, it pulls up three different quotes from the database at random. The database itself is managed with this application that allows you to go through and add, edit and delete entries in the database. We'll look at that in a separate movie in this chapter. In this chapter, we're going to look at how this application works ,which retrieves the quotes from the database and displays them at random.

Displaying random entries from a database

Here we have a simple database application that displays a list of random testimonials or quotes on a web page. If you look at my web page, I actually used this for testimonials. And every time the page gets reloaded, it pulls up three different quotes from the database at random. The database itself is managed with this application that allows you to go through and add, edit and delete entries in the database. We'll look at that in a separate movie in this chapter. In this chapter, we're going to look at how this application works ,which retrieves the quotes from the database and displays them at random.

So in the Projects folder, in your Exercise Files, in the testimonials folder and you'll find testimonials.py. And this is actually exactly the same script that is on my web site. This is the script that reads the quotes from the database and displays a number of them at random. It's a very short script. It's just 73 lines long, including the white space and comments and everything, and here's how it works. The first thing it does is it initializes some variables.

It reads the configuration file to find out where the database is and everything, and opens up the database. And all that happens here in this init function. Here it reads the configuration file there and it opens up the database here. And this uses libraries that I've also included in the Lib folder. bwDB for my normalized CRUD oriented database functions, and bwConfig for reading the configuration file.

bwConfig is a very simple library. It reads these configuration files in a format that I had already been using for a long time with my Perl work from before I was working on Python. And so I just wanted something that would read the same configuration file, so I could start replacing a lot of my Perl scripts with Python scripts, and it was just very easy for me to write that. And the application itself mostly takes place in this one function, in main. The first thing it does is it goes out to the database and it grabs a list of all the IDs, and it does this with this sql_query method which returns a generator which iterates through the results.

And iterating through results, I simply take all of these IDs and add them to this list here. I'm using a list because I need to be able to delete things from it later. So a tuple would have been immutable. Then I want to know how many records I'm going to be displaying and so I look for the query string and if there isn't a query string, that just default to five. And we'll notice, if we look at the HTML for the page that has those quotes on it, you'll notice this is called with this little bit of server side include and so it's called testimonials.py with a query string set to 3.

And so, that's why we have three of them displaying on that page. And then, I check and see if we have enough in the database to be able to display a decent number randomly. I like further to be at least four times as many records in the database as those that I am displaying. Otherwise I really don't want to bother doing something random because it's not going to look random. Now we simply take the list of IDs and using the random library, which gets imported up at the top here.

This is in the standard Python library. It creates a random integer based on the size of the list minus one, and it grabs a random item from the list of IDs, and then it deletes that from the list and adds it to the list of result IDs, which is initialized here. Then once it has that list of result IDs, it simply iterates through that list and prints the record with that ID. And printing a record with that ID, it uses the CRUD function getrec and then it simply grabs the data out of the resulting row factory, indexing on it as if it were a dictionary.

We'll go ahead and run this here. Well for our purposes, we're going to need to reduce this little default down to a three. So I'll save that and run it, and here we have our result. We have three quotes, and if we run it again, we get three different quotes and different quotes and you'll notice that it's all coming out in HTML. So, that's how this application works. Once we have done the back end work of creating the CRUD, once we have done the back end work of creating a decent library with easy to use database interface, writing something like this becomes relatively trivial.

And so, here we have it on the webpage with our random quotes.

Show transcript

This video is part of

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Python 3 Essential Training

87 video lessons · 37688 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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