Python设计模式编程中解释器模式的简单程序示例分享

模式特点：给定一个语言，定义它的文法的一种表示，并定义一个解释器，这个解释器使用该表示来解释语言中的句子。

我们来看一下下面这样的程序结构：

class Context:
  def __init__(self):
    self.input=""
    self.output=""

class AbstractExpression:
  def Interpret(self,context):
    pass

class 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)

那么它所体现出的类图是这样的：

再来看一个例子：

#encoding=utf-8
#
#by panda
#解释器模式 

def printInfo(info):
  print unicode(info, 'utf-8').encode('gbk'), 

#上下文类：演奏内容
class PlayContext():
  text = None
  PlayText = None 

#抽象表达式类
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(' ') #找出第一个空格出现的位置
      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();

类图：