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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _doCommandCompletion(self):
 """ Command-completion method """
        
        prefix =  ''.join(self.inputBuffer).strip().upper()
        matches = self.completion.keys(prefix)
        matchLen = len(matches)        
        if matchLen == 0 and prefix[-1] == '=':
            try:                
                command = prefix[:-1]
            except KeyError:
                pass                        
            else:
                self.__printCommandSyntax(command)
        elif matchLen > 0:                        
            if matchLen == 1:
                if matches[0] == prefix:
                    # User has already entered command - show command syntax
                    self.__printCommandSyntax(prefix)
                else:
                    # Complete only possible command
                    self.inputBuffer = list(matches[0])
                    self.cursorPos = len(self.inputBuffer)
                    self._refreshInputPrompt(len(self.inputBuffer))
                return
            else:
                commonPrefix = self.completion.longestCommonPrefix(''.join(self.inputBuffer))
                self.inputBuffer = list(commonPrefix)
                self.cursorPos = len(self.inputBuffer)
                if matchLen > 20:
                    matches = matches[:20]
                    matches.append('... ({0} more)'.format(matchLen - 20))
            sys.stdout.write('\n')
            for match in matches:
                sys.stdout.write(' {0} '.format(match))
            sys.stdout.write('\n')
            sys.stdout.flush()
            self._refreshInputPrompt(len(self.inputBuffer))