paul | Python Fiddle

class Dictionary1:
    """
        A dictionary represented with a Python list.
        Each list element is a tuple of two parts, the key and the value
    """
    def __init__(self):
        #precondition(True)
        self.__listOfPairs = []

# "extending" constructor method: 'with'
    #  d.withEntry(k, v) has all the key/value pairs of d, together with a new entry
    def withEntry(self, key, value):
        #precondition(True)
        result = Dictionary1()
        result.__listOfPairs = [ (key, value) ] + self.__listOfPairs
        return result

# axioms:
    #  Dictionary().lookup(x) === "No entry"
    #  d.withEntry(k, v).lookup(x) === v, if k==x
    #                          or d.lookup(x), otherwise
    def lookup(self, key):
        #precondition(True)
        for pair in self.__listOfPairs:
            if pair[0] == key:
                return pair[1]
        return "No entry"

# axioms:
    #  d.put(k, v) --> new d is d.withEntry(k, v)
    def put(self, key, value):
        #precondition(True)
        self.__listOfPairs = [ (key, value) ] + self.__listOfPairs

def __eq__(self,other):
        #precondition( isinstance(otherDictionary,Dictionary1) )
    	if len(self.rep) != len(other.rep):
            return False
        for x in self.rep, y in other.rep:
            if x != y or self.rep[x] != other.rep[y]:
                return False
        return True
    
    
    def __eq__(self,otherDictionary):
        precondition( isinstance(otherDictionary,Dictionary1) )
        if len(self.rep) != len(otherDictionary.rep):
            return False
        for x in self.rep, y in otherDictionary.rep:
            if x != y or self.rep[x] != otherDictionary.rep[y]:
                return False
        return True

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