Template inheritance

If no file extension is given,. Then, define one or more blocks to override the parent block content. As it shows, content now exposes a sidebar and primary block for overriding. Alternatively, the child template could override content altogether. Pug allows you to replace default , prepend , or append blocks. Suppose you have default scripts in a head block that you wish to use on every page. Article Contributed By :. Easy Normal Medium Hard Expert. Writing code in comment?

Please use ide. Load Comments. What's New. Most popular in Python. Too often we find ourselves forced to do the former, if only to hedge our bets. Efficient components make reuse a win-win choice, and some of the techniques discussed below can help library developers to build such components.

Policy classes provide either a different approach to the same problem based on application-specific criteria, or offer a different implementation of the same task. The difference between the two is more conceptual than concrete, but examining it in each case helps explain how it can be used in practice. An example of the first case is a class that comparisons of strings being used to sort strings. There are various different ways we can sort strings. The simplest way is a simple comparison of the numerical values of the characters.

There are case-sensitive and case-insensitive sort orders. There are case-insensitive sort orders that consider i equivalent to I and case-insensitive sort orders that consider i equivalent to İ. None of these differences in how we determine which string comes before which affects the rest of a sorting operation how we determine which to compare and how we move strings.

Hence it makes little sense to write different sort operations for case-sensitive sorts, case-insensitive sorts, and so on. This becomes even less sensible if, as well as offering a variety of sort criteria, we wish to offer a variety of sort algorithms, deal with a variety of character encodings, deal with different containers and make use of a swap operation that is efficient with a given datatype. This provides the necessary flexibility, but requires a function call for each comparison.

If we use a function object, and make the type of that function object a template parameter to the sort, then it becomes easier to inline the call to the comparison operation. A variant on this is a class whose, often static, members provide functionality to another class.

Similarly ATL provides a class to lock and unlock a thread, and another where the namesake member functions are dummy no operation functions that are optimised away entirely. This allows ATL to easily create thread-safe versions of a class without incurring overhead in cases where thread-safety is not needed, or is already provided by the COM apartment model.

Without templates virtual functions could be used to provide the same functionality. Consider the task of advancing an iterator by an arbitrary number of iterations. In the case of a random-access iterator including a pointer into an array this can be done in constant time, we simply add the appropriate number to the iterator:. With an input, or bi-directional iterator we cannot do this, and so we have to use the linear time method of incrementing the iterator a sufficient number of times:.

In each case we have the most efficient way of producing the desired result. However we have three separate functions depending on the type of iterator. The solution is to provide iterators with a tag member typedef. In a random access iterator we have the following public typedef:. Typically header, navigation, footer, and sidebar remains the same throughout the site. The problem arises when we want to modify some part of the page. To better understand the issue, let's take an example.

Let's say at the time of deployment the company decided to change the anchor text of a link in the navigation from Career to Jobs. To make this change we have to manually visit each and every page.

What if we had 50 or pages? These days it is very common for sites to have hundreds or even thousands of pages. As you can see this method doesn't scale very well. If you are reading all these pages carefully, you might say "Hey why don't we use include tag? Yes, sure we can use include tag to solve this particular problem very easily but as we will see Template Inheritance provides a much more powerful and elegant method to tackle issues like this.

Django Templates which we are going to create in the upcoming section are not specific to any app. In fact, any installed app in the project can use these templates. As already discussed, by default Django looks for templates in the templates directory of every installed app.

But Django doesn't define any default location to look for templates that are not specific to any app. Therefore, we can store these sitewide templates almost anywhere.

Now we have to inform Django about this directory. Open settings.