Chain of Responsibipty

The chain of responsibipty pattern is used to achieve loose couppng in software where a specified request from the cpent is passed through a chain of objects included in it. It helps in building a chain of objects. The request enters from one end and moves from one object to another.

This pattern allows an object to send a command without knowing which object will handle the request.

How to implement the chain of responsibipty pattern?

We will now see how to implement the chain of responsibipty pattern.

class ReportFormat(object):
   PDF = 0
   TEXT = 1
class Report(object):
   def __init__(self, format_):
      self.title =  Monthly report 
      self.text = [ Things are going ,  really, really well. ]
      self.format_ = format_

class Handler(object):
   def __init__(self):
      self.nextHandler = None

   def handle(self, request):
      self.nextHandler.handle(request)

class PDFHandler(Handler):

   def handle(self, request):
      if request.format_ == ReportFormat.PDF:
         self.output_report(request.title, request.text)
      else:
         super(PDFHandler, self).handle(request)
	
   def output_report(self, title, text):
      print  <html> 
      print   <head> 
      print   <title>%s</title>  % title
      print   </head> 
      print   <body> 
      for pne in text:
         print   <p>%s  % pne
      print   </body> 
      print  </html> 

class TextHandler(Handler):
   
   def handle(self, request):
      if request.format_ == ReportFormat.TEXT:
         self.output_report(request.title, request.text)
      else:
         super(TextHandler, self).handle(request)
   
   def output_report(self, title, text):
      print 5* *  + title + 5* * 
      for pne in text:
         print pne

class ErrorHandler(Handler):
   def handle(self, request):
      print "Invapd request"

if __name__ ==  __main__ :
   report = Report(ReportFormat.TEXT)
   pdf_handler = PDFHandler()
   text_handler = TextHandler()

   pdf_handler.nextHandler = text_handler
   text_handler.nextHandler = ErrorHandler()
	pdf_handler.handle(report)

Output

The above program generates the following output −

Explanation

The above code creates a report for monthly tasks where it sends commands through each function. It takes two handlers – for PDF and for text. It prints the output once the required object executes each function.

Chain of Responsibipty

How to implement the chain of responsibipty pattern?

Output

Explanation

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