diff --git a/src/hashtree.py b/src/hashtree.py
--- a/src/hashtree.py
+++ b/src/hashtree.py
@@ -11,28 +11,28 @@ def hashBlock(data):
 
 
 class HashTree:
-	HASH_LEN=16 # bytes
-	BLOCK_SIZE=4096 # bytes
+	HASH_LEN = 16 # bytes
+	BLOCK_SIZE = 4096 # bytes
 	
 	## Prepares a tree containing leafCount leaves.
-	def __init__(self,leafCount):
-		self.store=[b""]*(leafCount*2-1)
-		self.leafStart=leafCount-1
-		self.leafCount=leafCount
-		self._index=self.leafStart
+	def __init__(self, leafCount):
+		self.store = [b""]*(leafCount*2-1)
+		self.leafStart = leafCount-1
+		self.leafCount = leafCount
+		self._index = self.leafStart
 		
 	@classmethod
-	def fromFile(cls,filename):
-		with open(filename,"rb") as f:
-			stat=os.fstat(f.fileno())
-			size=stat.st_size # !! symlinks
-			leafCount=(size-1)//HashTree.BLOCK_SIZE+1 # number of leaf blocks
-			res=cls(leafCount)
+	def fromFile(cls, filename):
+		with open(filename, "rb") as f:
+			stat = os.fstat(f.fileno())
+			size = stat.st_size # !! symlinks
+			leafCount = (size-1)//HashTree.BLOCK_SIZE+1 # number of leaf blocks
+			res = cls(leafCount)
 			print(datetime.now(), "hashing file:")
 
-			progress=Progress(leafCount)
+			progress = Progress(leafCount)
 			for i in range(leafCount):
-				data=f.read(HashTree.BLOCK_SIZE)
+				data = f.read(HashTree.BLOCK_SIZE)
 				res.insertLeaf(hashBlock(data))
 
 				progress.p(i)
@@ -42,19 +42,19 @@ class HashTree:
 		return res
 
 	@classmethod
-	def load(cls,filename):
-		with open(filename,"rb") as f:
-			stat=os.fstat(f.fileno())
-			size=stat.st_size
-			nodeCount=size//HashTree.HASH_LEN
-			res=cls((nodeCount+1)//2)
+	def load(cls, filename):
+		with open(filename, "rb") as f:
+			stat = os.fstat(f.fileno())
+			size = stat.st_size
+			nodeCount = size//HashTree.HASH_LEN
+			res = cls((nodeCount+1)//2)
 
 			for i in range(nodeCount):
-				res.store[i]=f.read(HashTree.HASH_LEN)
+				res.store[i] = f.read(HashTree.HASH_LEN)
 		return res
 
-	def save(self,filename):
-		with open(filename,"wb") as f:
+	def save(self, filename):
+		with open(filename, "wb") as f:
 			for h in self.store:
 				f.write(h)
 		
@@ -62,43 +62,43 @@ class HashTree:
 	#
 	#	Useful and used only during the tree construction.
 	def insertLeaf(self,h):
-		self.store[self._index]=h
-		self._index+=1
+		self.store[self._index] = h
+		self._index += 1
 		
 	## Updates a hash stored in the leaf.
-	def updateLeaf(self,index,h):
+	def updateLeaf(self, index, h):
 		if index<self.leafStart: raise IndexError()
 		
-		self.store[index]=h
+		self.store[index] = h
 		self.updateNode((index-1)//2)
 	
 	## Updates the node at index and all its ancestors.
-	def updateNode(self,index):
+	def updateNode(self, index):
 		while index>=0:
-			self.store[index]=hashBlock(self.store[index*2+1]+self.store[index*2+2])
-			index=(index-1)//2
+			self.store[index] = hashBlock(self.store[index*2+1]+self.store[index*2+2])
+			index = (index-1)//2
 			
 	## Fast construction of the tree over the leaves. O(n).
 	def buildTree(self):
 		print(datetime.now(), "building tree:")
 		progress=Progress(-1, self.leafStart-1)
-		for i in range(self.leafStart-1,-1,-1):
-			self.store[i]=hashBlock(self.store[i*2+1]+self.store[i*2+2])
+		for i in range(self.leafStart-1, -1, -1):
+			self.store[i] = hashBlock(self.store[i*2+1]+self.store[i*2+2])
 			progress.p(i)
 		progress.done()
 
 	## Update faster than repeated insertLeaf.
-	def batchUpdate(self,keysHashes):
-		queue=collections.deque()
-		for (k,v) in sorted(keysHashes):
-			self.store[k]=v
-			parentK=(k-1)//2
+	def batchUpdate(self, keysHashes):
+		queue = collections.deque()
+		for (k, v) in sorted(keysHashes):
+			self.store[k] = v
+			parentK = (k-1)//2
 			if len(queue)==0 or queue[-1]!=parentK:
 				queue.append(parentK)
 
 		while len(queue)>0:
-			k=queue.pop()
-			self.store[k]=hashBlock(self.store[k*2+1]+self.store[k*2+2])
-			parentK=(k-1)//2
+			k = queue.pop()
+			self.store[k] = hashBlock(self.store[k*2+1]+self.store[k*2+2])
+			parentK = (k-1)//2
 			if (len(queue)==0 or queue[0]!=parentK) and k!=0:
 				queue.appendleft(parentK)