Adds _HashMapItem object that will be used to properly handle collisions.

Also adds documentation to the first HM implementation

02_hash_maps/hm.py

@@ -7,12 +7,27 @@ Collisions are not handled in this version.
 2013/11
 """
 
+class _HashMapItem():
+	"""
+	Hashmap items are the objects that will be contained in my Hashmaps.
+	They permit to find the correct value back, even in case of collision.
+	Not all of my HashMap implementations use HMItems.
+	"""
+	def __init__(self, key, value):
+		self.k = key
+		self.v = value
+
 class HashMap():
+	"""
+	This implementation does NOT use _HashMapItems
+	Also, this implementation will return an error in case of a collision.
+	Data will not be lost, but another key will have to be used.
+	"""
 	def __init__(self, hash_size=513):
 		self._hash_size = hash_size
 		self._size = 0
 		self.hmap = [None] * self._hash_size
-		
+
 	def add(self, key, value):
 		"""
 		Adds the provided value to the hashmap.
@@ -22,96 +37,96 @@ class HashMap():
 		if self.hmap[my_key] == None:
 			self.hmap[my_key] = value
 			self._size += 1
-		else: 
+		else:
 			raise Exception("Collision detected at index %d", key)
-		
+
 	def get(self, key):
 		"""
-		Finds the element in the hash table that may contain the id for 
+		Finds the element in the hash table that may contain the id for
 		the string we are looking for
 		"""
 		my_key = self._hash(key)
-		return self.hmap[my_key]		
+		return self.hmap[my_key]
-	
+
 	def size(self):
 		return self._size
-	
+
 	def _hash(self, value):
 		"""
 		Generates a hash for the given value.
 		The input is expected to be a String, with only ASCII characters.
-		
+
 		# hash function taken from HT3.
 		# We shift and add : << 4 is a *16
 		"""
 		if len(value) < 1:
 			raise Exception("Size of value must be greater than one")
-		
+
 		h = 0
 		for letter in value:
 			h = (h << 4) + ord(letter)
-			
+
 		return h % self._hash_size
 
 class HMTableCollision(HashMap):
 	"""
 	Extension of the previous HashMap implementation that takes care of
 	collisions.
-	Instead of having only one slot available per index in the table, 
+	Instead of having only one slot available per index in the table,
-	each index will contain a list. This means several elements can be 
+	each index will contain a list. This means several elements can be
 	stored with the same index.
 	"""
 	def __init__(self, hash_size=513):
 		self._hash_size = hash_size
 		self._size = 0
 		self.hmap = [None] * self._hash_size
-		
+
 	def add(self, key, value):
 		"""
 		Adds the provided value to the hashmap.
 		Raises an Exception if a collision is detected
 		"""
 		my_key = self._hash(key)
-					
+
 		if self.hmap[my_key] == None:
 			self.hmap[my_key] = [value]
-		else: 
+		else:
 			self.hmap[my_key].append(value)
 		self._size += 1
-	
+
 	def get(self, key):
 		"""
-		Finds the element in the hash table that may contain the id for 
+		Finds the element in the hash table that may contain the id for
 		the string we are looking for
 		"""
 		my_key = self._hash(key)
 		vals = self.hmap[my_key]
-		
+
 		if vals is None:
 			return vals
 		elif len(vals) == 1:
-			return vals[0] 
+			return vals[0]
 		else:
 			return vals # we return all the results if there are several
-	
+
 	def size(self):
 		return self._size
-	
+
 	def _hash(self, value):
 		"""
 		Generates a hash for the given value.
 		The input is expected to be a String, with only ASCII characters.
-		
+
 		# hash function taken from HT3.
 		# We shift and add : << 4 is a *16
 		"""
 		if len(value) < 1:
 			raise Exception("Size of value must be greater than one")
-		
+
 		h = 0
 		for letter in value:
 			h = (h << 4) + ord(letter)
-			
+
 		return h % self._hash_size
 
 class HMNeighbourCollision():
@@ -119,7 +134,7 @@ class HMNeighbourCollision():
 		self._hash_size = hash_size
 		self._size = 0
 		self.hmap = [None] * self._hash_size
-		
+
 	def add(self, key, value):
 		"""
 		Adds the provided value to the hashmap.
@@ -127,7 +142,7 @@ class HMNeighbourCollision():
 		"""
 		my_key = self._hash(key)
 		idx = self._find_free_idx(my_key)
-		
+
 		self.hmap[idx] = value
 		self._size += 1
 
@@ -139,7 +154,7 @@ class HMNeighbourCollision():
 		idx = key
 		cur_ptr = 1
 		negative = True
-		
+
 		while(True):
 			if self.hmap[idx] == None:
 				return idx
@@ -151,30 +166,30 @@ class HMNeighbourCollision():
 					idx = key + cur_ptr
 					negative = True
 					cur_ptr += 1
-		
+
 	def get(self, key):
 		"""
-		Finds the element in the hash table that may contain the id for 
+		Finds the element in the hash table that may contain the id for
 		the string we are looking for
 		"""
 		#TODO
-			
+
 	def size(self):
 		return self._size
-	
+
 	def _hash(self, value):
 		"""
 		Generates a hash for the given value.
 		The input is expected to be a String, with only ASCII characters.
-		
+
 		# hash function taken from HT3.
 		# We shift and add : << 4 is a *16
 		"""
 		if len(value) < 1:
 			raise Exception("Size of value must be greater than one")
-		
+
 		h = 0
 		for letter in value:
 			h = (h << 4) + ord(letter)
-			
+
 		return h % self._hash_size