class WebBrowser:

def $\_\_$init$\_\_($self$,$ page$)$:

self.history $=[$page$]$

self.current$\_$page $=$ page

self.is$\_$incognito $=$ False

def navigate$($self$,$ new$\_$page$)$:

self.current$\_$page $=$ new$\_$page

if not self.is$\_$incognito:

self.history.append$($new$\_$page$)$

def clear$\_$history$($self$)$:

self.history$[$:$-1]=[]$

@classmethod

def with$\_$incognito$($cls$,$ page$)$:

instance $=$ cls$($page$)$

instance.is$\_$incognito $=$ True

instance.history $=[]$

return instance

The WebBrowser class

Print out the class method as shown in Snippet $7\mathrm{.}53.$ The output tells us that it is a bound method of the WebBrowser class. This illustrates what we said earlier regarding class methods and how they are bound to the class itself:

$>>>$ from main import WebBrowser

$>>>$ WebBrowser.with$\_$incognito

$>$

Snippet $7\mathrm{.}53$

Create a WebBrowser instance that starts off in incognito mode. Note that we call with$\_$incognito through the class. Despite not passing the cls argument in this call, Python implicitly passes the WebBrowser class to the function. All we need to pass in is the page parameter as shown in Snippet $7\mathrm{.}54$:

$>>>$ chrome $=$ WebBrowser.with$\_$incognito$("$shady$-$website.com"$)$

$>>>$ chrome.is$\_$incognito

True

Snippet $7\mathrm{.}54$

Print out the current page of our instance to check whether it was set as shown in Snippet $7\mathrm{.}55$:

$>>>$ chrome.current$\_$page

'shady$-$website.com'

Snippet $7\mathrm{.}55$

Confirm that the history was not tracked as shown in Snippet $7\mathrm{.}56$:

$>>>$ chrome.history

$[]$

$>>>$

Snippet $7\mathrm{.}56$

Additionally, you can call class methods through instances for the same effect as shown in Snippet $7\mathrm{.}57$:

$>>>$ opera $=$ WebBrowser$("$foobar$.$com"$)$

$>>>$ netscape $=$ opera.with$\_$incognito$("$secret$.$net"$)$

$>>>$ netscape.current$\_$page

'secret.net'

$>>>$ netscape.is$\_$incognito

True

$>>>$

Snippet $7\mathrm{.}57$

You should only call class methods through an instance in situations where it won't raise any confusion as to what kind of method it is you're calling $($instance or class method$).$

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