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Customizing Django Templates

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Custom Time Estimate Filter

3:36 with Lacey Williams Henschel

This filter will help you estimate how much time it will take a person to complete a particular step in a course on your site.

Django documentation on custom template filters

pluralize - A filter that, by default, returns an "s" when attached to a number that's not 1, and nothing when the number is 1. You can provide different options if needed. More information is available in the official documentation.

register.filter("filter_name", filter_function) or @register.filter("filter_name") - Registers a filter with the given name.

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    [SOUND] You've made it to the last stage of this course, 0:00
    but it's not time to celebrate just yet. 0:06
    We still have a few more things to learn before you finally get your shiny new 0:11
    Django templates badge. 0:15
    In this video, we're going to build our own custom template filter 0:18
    that we can use on variables just like built-in filters. 0:22
    Remember, a filter is something that you can add to a Django template variable 0:26
    with the pipe character, that helps make the data in your template more dynamic. 0:30
    In the case of the pluralized filter, 0:35
    you learned in another video that it can automatically make a word plural 0:38
    based on the value of a numeric variable in the template. 0:42
    So let's write a filter that will help us estimate how much 0:46
    time a step in a course will take to complete. 0:50
    So let's open up the file we've been keeping our custom template tags in, 0:54
    course_extras.py. 0:57
    This is where we'll also be adding our custom filter. 0:58
    Make a new function called, time_estimate, and have it take in a value. 1:02
    So, define time_estimate, and I'm going to call my value, word_count. 1:06
    In our case, this value will be a number, the number of words in a steps content. 1:14
    This filter is not going to be super scientific. 1:18
    This is mostly a thought exercise. 1:21
    But let's say that the longer a steps content is, 1:24
    the more content we think it covers and the more time we think it will take. 1:27
    So with that in mind, let's say that for every 20 words in a steps content, 1:32
    we think it will take that many minutes to complete the course. 1:37
    So let's code that. 1:41
    So minutes = round(word_count/20). 1:43
    We're using the round function here, which is a built-in Python function, so 1:50
    we get a nice even number. 1:54
    We don't want to display 5.4567 minutes, do we? 1:56
    This is just an estimate. 2:01
    So we estimate that for every 20 words in a word count, 2:03
    it will take about a minute to complete that part of the step. 2:08
    Now, we just need to return the minutes. 2:12
    And we should add a docstring so 2:15
    that everyone else who looks at our code knows what this filter does. 2:17
    So we can say, Estimates the number of minutes it will take 2:21
    to complete a step based on the passed-in wordcount. 2:27
    Finally, we need to register the filter. 2:36
    Registering filters is almost the same as registering tags. 2:39
    We use the decorator, and then instead of saying .inclusiontag or .simpletag, 2:43
    we just say .filter and pass in the name of our filter. 2:49
    Now we can try it out. 2:55
    If we pop over to step detail, we can load our 2:57
    course_extras so that we have access to our brand new filter. 3:02
    But wait a second, we don't have a variable for 3:07
    the word count that we've passed-in from our view. 3:10
    Let's see what we can do about that in the next video. 3:14
    Well, we made our filter but we need to figure out how to use it. 3:19
    Are you thinking what I'm thinking? 3:24
    What if there's a way we can use the built-in word count filter 3:26
    to get the data we need for this filter? 3:30
    Let's find out in the next video. 3:33

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