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<title>8. Using OOP to program a website</title>
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<H1><A NAME="SECTION0010000000000000000000">
8. Using OOP to program a website</A>
</H1>
<P>
One the the most powerful feature of CherryPy is that you can really use an <b>object oriented</b> approach
to "program" your website.
<P>
When you look at a complex website, you'll realize that some parts have a lot in common:
<UL>
<LI>They use the same functionalities but these functionalities are applied to a different type of data
</LI>
<LI>They display the same information, but the data is displayed differently (for instance, when you have multiple versions of a website, or you have several
versions in several languages)
</LI>
</UL>
<P>
In both cases, OOP provides an elegant solution to the problem and minimizes the amount of code that is required to
implement the solution.
<P>
To show you how this can be done, we'll create a website that comes in two versions: the English version
and the French version. Not only do the text and labels change, but also the colors and the way modules are displayed.
<P>
Enter the following code for the website:
<div class="verbatim"><pre>
#######################
CherryClass Airline abstract:
#######################
function:
def localize(self, stri):
return self.dictionnary.get(stri, stri)
mask:
def header(self):
<html><body>
<center>
<H1 py-eval="self.localize('Welcome to CherryPy airline')"></H1>
<div py-if="self==airlineFrench">
<a py-attr="request.base+'/airlineEnglish/index'" href="">
Click here for English version
</a>
</div><div py-else>
<a py-attr="request.base+'/airlineFrench/index'" href="">
Cliquez ici pour la version française
</a>
</div>
<br><br><br><br>
def footer(self):
</center>
</body></html>
def squareWithText(self, title, text):
<table border=0 cellspacing=0 cellpadding=1 width=200><tr>
<td py-attr="self.borderColor" bgColor="">
<table border=0 cellspacing=0 cellpadding=5><tr>
<td py-attr="self.insideColor" bgColor=""
align=center width=198 py-eval="'<b>%s</b><br><br>%s'%(title,text)">
</td>
</tr></table>
</td>
</tr></table>
view:
def bookAFlight(self):
page=self.header()
page+=self.squareWithText(self.localize('Booking a flight'),
self.localize('To book a flight, think about where you want to go, and you should dream about it tonight'))
page+=self.footer()
return page
#######################
CherryClass AirlineFrench(Airline):
#######################
variable:
insideColor='#FFFF99'
borderColor='#FF6666'
dictionnary={
'Welcome to CherryPy airline': 'Bienvenue chez CherryPy airline',
'Booking a flight': 'Rserver un vol',
'To book a flight, think about where you want to go, and you should dream about it tonight':
'Pour rserver un vol, pensez trs fort la destination, et vous devriez en rver cette nuit'
}
view:
def index(self):
page=self.header()
page+=self.squareWithText('Rserver un vol', 'Pour rserver un vol, cliquez sur <a href="%s/bookAFlight">réserver</a>'%self.getPath())+'<br>'
page+=self.squareWithText('Prsentation', 'CherryPy airline est la compagnie qui vous emmne au 7me ciel')
page+=self.footer()
return page
#######################
CherryClass AirlineEnglish(Airline):
#######################
variable:
insideColor='#00CCFF'
borderColor='#3333FF'
dictionnary={}
view:
def index(self):
page=self.header()
page+=self.squareWithText('Presentation', 'CherryPy airline is the company that will take you to cloud 9')+'<br>'
page+=self.squareWithText('Book a flight', '<a href="%s/bookAFlight">Click here</a> to book a flight'%self.getPath())
page+=self.footer()
return page
#######################
CherryClass Root(AirlineEnglish):
#######################
</pre></div>
<P>
This program uses a lot of new features of CherryPy. Let's try to understand how it works:
<P>
The idea is to use a generic CherryClass (<var>Airline</var>) that contains functions, masks and views that are
common to both versions (English and French) or the website. Then we use 2 CherryClasses (<var>AirlineFrench</var>
and <var>AirlineEnglish</var>) to implement specificities of each version.
<P>
We use two different ways to implement specificities of each version:
<UL>
<LI>Either the only difference is the labels (they are translated into French for the French version). In this case,
we just use a dictionnary to implement the translation.
</LI>
<LI>Or the presentation of the information also changes. In this case, we write 2 versions of each method.
</LI>
</UL>
<P>
This example also shows some new features of CherryPy:
<P>
<UL>
<LI><b>Abstract CherryClasses</b>: in this example, you'll notice that CherryClass <var>Airline</var> is declared "abstract". This
just means that the server won't create any instance of the CherryClass called <var>airline</var>. As a result, you can't
use the URL <a class="url" href="http://localhost:8000/airline/index">http://localhost:8000/airline/index</a>. The idea behind this is that <var>Airline</var> cannot be used directly.
It has to be derived into sub-classes, and only these sub-classes can be accessed from the browser.
</LI>
<LI><b>Variable section</b>: you'll notice that this example uses a new kind of section in a CherryClass: <var>variable</var>. This
is just used to set variables by default for this CherryClass.
</LI>
<LI><b>self.getPath()</b>: by default, CherryPy creates a method called <var>getPath</var> for each CherryClass. This method returns
the URL of the CherryClass. For instance, for the <var>AirlineFrench</var> CherryClass, <var>getPath</var> would return
<a class="url" href="http://localhost:8000/airlineFrench">http://localhost:8000/airlineFrench</a>.
<P>
This method also takes an optional argument <var>includeRequestBase</var>, which defaults to 1. If you set it to 0 then the returned URL won't include the domain name.
For instance, for the <var>AirlineFrench</var> CherryClass, <var>getPath(0)</var> would return
<a class="url" href="/airlineFrench">/airlineFrench</a>.
</LI>
</UL>
<P>
In the next chapter, we'll learn how to split our code in several source files...
<P>
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<span class="release-info">Release 0.10, documentation updated on 19 March 2004.</span>
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