模式特點(diǎn)：給定一個(gè)語(yǔ)言，定義它的文法的一種表示，并定義一個(gè)解釋器，這個(gè)解釋器使用該表示來(lái)解釋語(yǔ)言中的句子。
我們來(lái)看一下下面這樣的程序結(jié)構(gòu)：
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class Context: def __init__(self): self.input="" self.output=""class AbstractExpression: def Interpret(self,context): passclass Expression(AbstractExpression): def Interpret(self,context): print "terminal interpret"class NonterminalExpression(AbstractExpression): def Interpret(self,context): print "Nonterminal interpret"if __name__ == "__main__": context= "" c = [] c = c + [Expression()] c = c + [NonterminalExpression()] c = c + [Expression()] c = c + [Expression()] for a in c: a.Interpret(context) |
那么它所體現(xiàn)出的類圖是這樣的：
再來(lái)看一個(gè)例子：
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#encoding=utf-8 # #by panda def printInfo(info): print unicode(info, 'utf-8').encode('gbk'), #上下文類：演奏內(nèi)容 class PlayContext(): text = None PlayText = None #抽象表達(dá)式類 class Expression(): def Interpret(self, context): if len(context.PlayText) == 0: return else: playKey = context.PlayText[0:1] context.PlayText = context.PlayText[2:] tmp = context.PlayText.index(' ') #找出第一個(gè)空格出現(xiàn)的位置 playValue = context.PlayText[0:tmp] context.PlayText = context.PlayText[tmp+1:] self.Excute(playKey,playValue) def Excute(self,playKey,playValue): pass #音高 class Pitch(Expression): pitch = None def Excute(self, key, value): value = int(value) if value == 1: self.pitch = '低音' elif value == 2: self.pitch = '中音' elif value == 3: self.pitch = '高音' printInfo(self.pitch) #音符 class Note(Expression): Notes = { 'C':1, 'D':2, 'E':3, 'F':4, 'G':5, 'A':6, 'B':7, } note = None def Excute(self, key, value): self.note = self.Notes[key] printInfo('%d' % self.note) def clientUI(): context = PlayContext() context.PlayText = "O 2 E 0.5 G 0.5 A 3 E 0.5 G 0.5 D 3 E 0.5 G 0.5 A 0.5 O 3 C 1 O 2 A 0.5 G 1 C 0.5 E 0.5 D 3 " expression = None; while(len(context.PlayText) > 0): str = context.PlayText[0:1]; if(str == 'O'): expression = Pitch() elif(str == 'C' or str == 'D' or str == 'E' or str == 'F' or str == 'G' or str == 'A' or str == 'B' or str == 'P'): expression = Note() expression.Interpret(context) return if __name__ == '__main__': clientUI(); |
類圖：
