Source Code for Module lepl.support.state

  1   
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 11  # 
 12  # The Original Code is LEPL (http://www.acooke.org/lepl) 
 13  # The Initial Developer of the Original Code is Andrew Cooke. 
 14  # Portions created by the Initial Developer are Copyright (C) 2009-2010 
 15  # Andrew Cooke (andrew@acooke.org). All Rights Reserved. 
 16  # 
 17  # Alternatively, the contents of this file may be used under the terms 
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 29   
 30  ''' 
 31  Encapsulate global (per thread) state. 
 32   
 33  This is for state that can affect the current parse.  It's probably simplest to 
 34  explain an example of what it can be used for.  Memoization records results 
 35  for a particular state to avoid repeating matches needlessly.  The state used 
 36  to identify when "the same thing is happening" is based on: 
 37  - the matcher being called 
 38  - the stream passed to the matcher 
 39  - this state 
 40   
 41  So a good shorthand for deciding whether or not this state should be used is 
 42  to ask whether the state will affect whether or not memoisation will work 
 43  correctly. 
 44   
 45  For example, with offside parsing, the current indentation level should be 
 46  stored here, because a (matcher, stream) combination that has previously failed 
 47  may work correctly when it changes.  
 48  ''' 
 49   
 50  from threading import local 
 51   
 52  from lepl.support.lib import singleton 
 53   
 54   
 55 -class State(local): 
 56      ''' 
 57      A thread local map from key (typically calling class) to value.  The hash 
 58      attribute is updated on each mutation and cached for rapid access.  
 59      ''' 
 60       
 61 -    def __init__(self): 
 62          ''' 
 63          Do not call directly - use the singleton. 
 64          ''' 
 65          super(State, self).__init__() 
 66          self.__map = {} 
 67          self.hash = self.__hash() 
 68           
 69      @classmethod 
 70 -    def singleton(cls): 
 71          ''' 
 72          Get a singleton instance. 
 73          ''' 
 74          return singleton(cls) 
 75       
 76 -    def __hash(self): 
 77          ''' 
 78          Calculate the hash for the current dict. 
 79          ''' 
 80          value = 0 
 81          for key in self.__map: 
 82              value ^= hash(key) ^ hash(self.__map[key]) 
 83          return value 
 84           
 85 -    def __getitem__(self, key): 
 86          return self.__map[key] 
 87       
 88 -    def get(self, key, default=None): 
 89          ''' 
 90          As for dict (lookup with default). 
 91          ''' 
 92          return self.__map.get(key, default) 
 93       
 94 -    def __setitem__(self, key, value): 
 95          self.__map[key] = value 
 96          self.hash = self.__hash() 
 97       
 98 -    def __delitem__(self, key): 
 99          del self.__map[key] 
100          self.hash = self.__hash() 
101          
102 -    def __hash__(self): 
103          return self.hash 
104