def start(self):
        ''' Method used to start the execution of this Task. self.command will
            be executed using the subprocess.Popen constructor with shell=True.
        '''
        if(self.stderr is not None):
            err = open(self.stderr, 'w', 1)
            err.write(str(self.command) + '\n\n')
            self.opened_files.append(err)
        else:
            err = None
        if(self.stdout is not None):
            out = open(self.stdout, 'w', 1)
            out.write(str(self.command) + '\n\n')
            self.opened_files.append(out)
        else:
            out = None
        self.start_time = time.time()
        temp = subprocess.Popen(self.command, shell=True, stdout=out, stderr=err)
        self.process = temp