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= Introduction =
Note: this page is an incomplete draft; please see IntroToPeak for a tutorial.
PEAK is an excellent platform for building Python database applications. Using a combination of several PEAK packages one can build powerful and flexible database applications quickly and easily.
= First Steps: Binding and Naming =
This small example is already a working database application. It opens a connection to a [http://www.sqlite.org/ SQLite] database file, runs a query against a table, and prints the results. It also demonstrates one of the most useful aspects of the binding package: the ability to create an object once and make use of it in another part of the application. In database applications you usually want a single connection to a database server which will be shared throughout the application. Without binding one would have to either create the connection object and pass it to every new object that needed it, or provide it to the rest of the application using a singleton mechanism of some kind.
The former technique is highly error prone and forces the application to be "tightly coupled" -- that is, objects need to know quite a bit about each other and are usually highly dependent on each other's interfaces and structure. Changing one object in a tightly coupled application often requires changes to a number of other objects, and in large applications these inter-dependencies are not always known by every programmer or are easily missed. Tightly coupled software tends to be extremely brittle as a result.
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The singleton approach can help quite a bit by ensuring that only one instance of a certain type of object exists and that it can be found relatively easily. In Python this is often achieved through a separate module and module-level variables. The great drawback of a singleton, however, is that there's only one of it. Classes that use singletons are less reusable, because you can't create instances that use different values for a singleton. (Because then it wouldn't be a singleton!) So, classes that use singletons are still tightly coupled.
What is typically needed in larger applications is a flexible way to create, lookup, and use "singleton-like" objects. PEAK calls such objects "service components", and part of what PEAK's `binding` package provides is easy access to such components, using looser forms of coupling such as:
