diff --git a/lang/zh/gklearn/kernels/treeletKernel.py b/lang/zh/gklearn/kernels/treeletKernel.py
new file mode 100644
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+++ b/lang/zh/gklearn/kernels/treeletKernel.py
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+"""
+@author: linlin
+
+@references: 
+
+	[1] Gaüzère B, Brun L, Villemin D. Two new graphs kernels in 
+	chemoinformatics. Pattern Recognition Letters. 2012 Nov 1;33(15):2038-47.
+"""
+
+import sys
+import time
+from collections import Counter
+from itertools import chain
+from functools import partial
+from multiprocessing import Pool
+from tqdm import tqdm
+
+import networkx as nx
+import numpy as np
+
+from gklearn.utils.graphdataset import get_dataset_attributes
+from gklearn.utils.parallel import parallel_gm
+
+def treeletkernel(*args, 
+				  sub_kernel, 
+				  node_label='atom', 
+				  edge_label='bond_type', 
+				  parallel='imap_unordered',
+				  n_jobs=None, 
+				  chunksize=None,
+				  verbose=True):
+	"""Calculate treelet graph kernels between graphs.
+
+	Parameters
+	----------
+	Gn : List of NetworkX graph
+		List of graphs between which the kernels are calculated.
+	
+	G1, G2 : NetworkX graphs
+		Two graphs between which the kernel is calculated.
+
+	sub_kernel : function
+		The sub-kernel between 2 real number vectors. Each vector counts the
+		numbers of isomorphic treelets in a graph.
+
+	node_label : string
+		Node attribute used as label. The default node label is atom.   
+
+	edge_label : string
+		Edge attribute used as label. The default edge label is bond_type.
+
+	parallel : string/None
+		Which paralleliztion method is applied to compute the kernel. The 
+		Following choices are available:
+
+		'imap_unordered': use Python's multiprocessing.Pool.imap_unordered
+		method.
+
+		None: no parallelization is applied.
+
+	n_jobs : int
+		Number of jobs for parallelization. The default is to use all 
+		computational cores. This argument is only valid when one of the 
+		parallelization method is applied.
+
+	Return
+	------
+	Kmatrix : Numpy matrix
+		Kernel matrix, each element of which is the treelet kernel between 2 praphs.
+	"""
+	# pre-process
+	Gn = args[0] if len(args) == 1 else [args[0], args[1]]
+	Gn = [g.copy() for g in Gn]
+	Kmatrix = np.zeros((len(Gn), len(Gn)))
+	ds_attrs = get_dataset_attributes(Gn,
+		attr_names=['node_labeled', 'edge_labeled', 'is_directed'],
+		node_label=node_label, edge_label=edge_label)
+	labeled = False
+	if ds_attrs['node_labeled'] or ds_attrs['edge_labeled']:
+		labeled = True
+		if not ds_attrs['node_labeled']:
+			for G in Gn:
+				nx.set_node_attributes(G, '0', 'atom')
+		if not ds_attrs['edge_labeled']:
+			for G in Gn:
+				nx.set_edge_attributes(G, '0', 'bond_type')
+	
+	start_time = time.time()
+	
+	# ---- use pool.imap_unordered to parallel and track progress. ----
+	if parallel == 'imap_unordered':
+		# get all canonical keys of all graphs before calculating kernels to save 
+		# time, but this may cost a lot of memory for large dataset.
+		pool = Pool(n_jobs)
+		itr = zip(Gn, range(0, len(Gn)))
+		if chunksize is None:
+			if len(Gn) < 100 * n_jobs:
+				chunksize = int(len(Gn) / n_jobs) + 1
+			else:
+				chunksize = 100
+		canonkeys = [[] for _ in range(len(Gn))]
+		get_partial = partial(wrapper_get_canonkeys, node_label, edge_label, 
+								labeled, ds_attrs['is_directed'])
+		if verbose:
+			iterator = tqdm(pool.imap_unordered(get_partial, itr, chunksize),
+							desc='getting canonkeys', file=sys.stdout)
+		else:
+			iterator = pool.imap_unordered(get_partial, itr, chunksize)
+		for i, ck in iterator:
+			canonkeys[i] = ck
+		pool.close()
+		pool.join()
+		
+		# compute kernels.
+		def init_worker(canonkeys_toshare):
+			global G_canonkeys
+			G_canonkeys = canonkeys_toshare
+		do_partial = partial(wrapper_treeletkernel_do, sub_kernel)
+		parallel_gm(do_partial, Kmatrix, Gn, init_worker=init_worker, 
+					glbv=(canonkeys,), n_jobs=n_jobs, chunksize=chunksize, verbose=verbose)
+		
+	# ---- do not use parallelization. ----
+	elif parallel == None:
+		# get all canonical keys of all graphs before calculating kernels to save 
+		# time, but this may cost a lot of memory for large dataset.
+		canonkeys = []
+		for g in (tqdm(Gn, desc='getting canonkeys', file=sys.stdout) if verbose else Gn):
+			canonkeys.append(get_canonkeys(g, node_label, edge_label, labeled, 
+										   ds_attrs['is_directed']))
+		
+		# compute kernels.
+		from itertools import combinations_with_replacement
+		itr = combinations_with_replacement(range(0, len(Gn)), 2)
+		for i, j in (tqdm(itr, desc='getting canonkeys', file=sys.stdout) if verbose else itr):
+			Kmatrix[i][j] = _treeletkernel_do(canonkeys[i], canonkeys[j], sub_kernel)
+			Kmatrix[j][i] = Kmatrix[i][j] # @todo: no directed graph considered?
+			
+	else:
+		raise Exception('No proper parallelization method designated.')
+
+	
+	run_time = time.time() - start_time
+	if verbose:
+		print("\n --- treelet kernel matrix of size %d built in %s seconds ---" 
+			  % (len(Gn), run_time))
+		
+	return Kmatrix, run_time
+
+
+def _treeletkernel_do(canonkey1, canonkey2, sub_kernel):
+	"""Calculate treelet graph kernel between 2 graphs.
+	
+	Parameters
+	----------
+	canonkey1, canonkey2 : list
+		List of canonical keys in 2 graphs, where each key is represented by a string.
+		
+	Return
+	------
+	kernel : float
+		Treelet Kernel between 2 graphs.
+	"""
+	keys = set(canonkey1.keys()) & set(canonkey2.keys()) # find same canonical keys in both graphs
+	vector1 = np.array([(canonkey1[key] if (key in canonkey1.keys()) else 0) for key in keys])
+	vector2 = np.array([(canonkey2[key] if (key in canonkey2.keys()) else 0) for key in keys]) 
+	kernel = sub_kernel(vector1, vector2) 
+	return kernel
+
+
+def wrapper_treeletkernel_do(sub_kernel, itr):
+	i = itr[0]
+	j = itr[1]
+	return i, j, _treeletkernel_do(G_canonkeys[i], G_canonkeys[j], sub_kernel)
+
+
+def get_canonkeys(G, node_label, edge_label, labeled, is_directed):
+	"""Generate canonical keys of all treelets in a graph.
+	
+	Parameters
+	----------
+	G : NetworkX graphs
+		The graph in which keys are generated.
+	node_label : string
+		node attribute used as label. The default node label is atom.		
+	edge_label : string
+		edge attribute used as label. The default edge label is bond_type.
+	labeled : boolean
+		Whether the graphs are labeled. The default is True.
+		
+	Return
+	------
+	canonkey/canonkey_l : dict
+		For unlabeled graphs, canonkey is a dictionary which records amount of 
+		every tree pattern. For labeled graphs, canonkey_l is one which keeps 
+		track of amount of every treelet.
+	"""
+	patterns = {} # a dictionary which consists of lists of patterns for all graphlet.
+	canonkey = {} # canonical key, a dictionary which records amount of every tree pattern.
+
+	### structural analysis ###
+	### In this section, a list of patterns is generated for each graphlet, 
+	### where every pattern is represented by nodes ordered by Morgan's 
+	### extended labeling.
+	# linear patterns
+	patterns['0'] = G.nodes()
+	canonkey['0'] = nx.number_of_nodes(G)
+	for i in range(1, 6): # for i in range(1, 6):
+		patterns[str(i)] = find_all_paths(G, i, is_directed)
+		canonkey[str(i)] = len(patterns[str(i)])
+
+	# n-star patterns
+	patterns['3star'] = [[node] + [neighbor for neighbor in G[node]] for node in G.nodes() if G.degree(node) == 3]
+	patterns['4star'] = [[node] + [neighbor for neighbor in G[node]] for node in G.nodes() if G.degree(node) == 4]
+	patterns['5star'] = [[node] + [neighbor for neighbor in G[node]] for node in G.nodes() if G.degree(node) == 5]		
+	# n-star patterns
+	canonkey['6'] = len(patterns['3star'])
+	canonkey['8'] = len(patterns['4star'])
+	canonkey['d'] = len(patterns['5star'])
+
+	# pattern 7
+	patterns['7'] = [] # the 1st line of Table 1 in Ref [1]
+	for pattern in patterns['3star']:
+		for i in range(1, len(pattern)): # for each neighbor of node 0
+			if G.degree(pattern[i]) >= 2:
+				pattern_t = pattern[:]
+				# set the node with degree >= 2 as the 4th node
+				pattern_t[i], pattern_t[3] = pattern_t[3], pattern_t[i]
+				for neighborx in G[pattern[i]]:
+					if neighborx != pattern[0]:
+						new_pattern = pattern_t + [neighborx]
+						patterns['7'].append(new_pattern)
+	canonkey['7'] = len(patterns['7'])
+
+	# pattern 11
+	patterns['11'] = [] # the 4th line of Table 1 in Ref [1]
+	for pattern in patterns['4star']:
+		for i in range(1, len(pattern)):
+			if G.degree(pattern[i]) >= 2:
+				pattern_t = pattern[:]
+				pattern_t[i], pattern_t[4] = pattern_t[4], pattern_t[i]
+				for neighborx in G[pattern[i]]:
+					if neighborx != pattern[0]:
+						new_pattern = pattern_t + [ neighborx ]
+						patterns['11'].append(new_pattern)
+	canonkey['b'] = len(patterns['11'])
+
+	# pattern 12
+	patterns['12'] = [] # the 5th line of Table 1 in Ref [1]
+	rootlist = [] # a list of root nodes, whose extended labels are 3
+	for pattern in patterns['3star']:
+		if pattern[0] not in rootlist: # prevent to count the same pattern twice from each of the two root nodes
+			rootlist.append(pattern[0])
+			for i in range(1, len(pattern)):
+				if G.degree(pattern[i]) >= 3:
+					rootlist.append(pattern[i])
+					pattern_t = pattern[:]
+					pattern_t[i], pattern_t[3] = pattern_t[3], pattern_t[i]
+					for neighborx1 in G[pattern[i]]:
+						if neighborx1 != pattern[0]:
+							for neighborx2 in G[pattern[i]]:
+								if neighborx1 > neighborx2 and neighborx2 != pattern[0]:
+									new_pattern = pattern_t + [neighborx1] + [neighborx2]
+#						 new_patterns = [ pattern + [neighborx1] + [neighborx2] for neighborx1 in G[pattern[i]] if neighborx1 != pattern[0] for neighborx2 in G[pattern[i]] if (neighborx1 > neighborx2 and neighborx2 != pattern[0]) ]
+									patterns['12'].append(new_pattern)
+	canonkey['c'] = int(len(patterns['12']) / 2)
+
+	# pattern 9
+	patterns['9'] = [] # the 2nd line of Table 1 in Ref [1]
+	for pattern in patterns['3star']:
+		for pairs in [ [neighbor1, neighbor2] for neighbor1 in G[pattern[0]] if G.degree(neighbor1) >= 2 \
+			for neighbor2 in G[pattern[0]] if G.degree(neighbor2) >= 2 if neighbor1 > neighbor2 ]:
+			pattern_t = pattern[:]
+			# move nodes with extended labels 4 to specific position to correspond to their children
+			pattern_t[pattern_t.index(pairs[0])], pattern_t[2] = pattern_t[2], pattern_t[pattern_t.index(pairs[0])]
+			pattern_t[pattern_t.index(pairs[1])], pattern_t[3] = pattern_t[3], pattern_t[pattern_t.index(pairs[1])]
+			for neighborx1 in G[pairs[0]]:
+				if neighborx1 != pattern[0]:
+					for neighborx2 in G[pairs[1]]:
+						if neighborx2 != pattern[0]:
+							new_pattern = pattern_t + [neighborx1] + [neighborx2]
+							patterns['9'].append(new_pattern)
+	canonkey['9'] = len(patterns['9'])
+
+	# pattern 10
+	patterns['10'] = [] # the 3rd line of Table 1 in Ref [1]
+	for pattern in patterns['3star']:		
+		for i in range(1, len(pattern)):
+			if G.degree(pattern[i]) >= 2:
+				for neighborx in G[pattern[i]]:
+					if neighborx != pattern[0] and G.degree(neighborx) >= 2:
+						pattern_t = pattern[:]
+						pattern_t[i], pattern_t[3] = pattern_t[3], pattern_t[i]
+						new_patterns = [ pattern_t + [neighborx] + [neighborxx] for neighborxx in G[neighborx] if neighborxx != pattern[i] ]
+						patterns['10'].extend(new_patterns)
+	canonkey['a'] = len(patterns['10'])
+
+	### labeling information ###
+	### In this section, a list of canonical keys is generated for every 
+	### pattern obtained in the structural analysis section above, which is a 
+	### string corresponding to a unique treelet. A dictionary is built to keep
+	### track of the amount of every treelet.
+	if labeled == True:
+		canonkey_l = {} # canonical key, a dictionary which keeps track of amount of every treelet.
+
+		# linear patterns
+		canonkey_t = Counter(list(nx.get_node_attributes(G, node_label).values()))
+		for key in canonkey_t:
+			canonkey_l[('0', key)] = canonkey_t[key]
+
+		for i in range(1, 6): # for i in range(1, 6):
+			treelet = []
+			for pattern in patterns[str(i)]:
+				canonlist = list(chain.from_iterable((G.nodes[node][node_label], \
+					G[node][pattern[idx+1]][edge_label]) for idx, node in enumerate(pattern[:-1])))
+				canonlist.append(G.nodes[pattern[-1]][node_label])
+				canonkey_t = canonlist if canonlist < canonlist[::-1] else canonlist[::-1]
+				treelet.append(tuple([str(i)] + canonkey_t))
+			canonkey_l.update(Counter(treelet))
+
+		# n-star patterns
+		for i in range(3, 6):
+			treelet = []
+			for pattern in patterns[str(i) + 'star']:
+				canonlist = [tuple((G.nodes[leaf][node_label], 
+									G[leaf][pattern[0]][edge_label])) for leaf in pattern[1:]]
+				canonlist.sort()
+				canonlist = list(chain.from_iterable(canonlist))
+				canonkey_t = tuple(['d' if i == 5 else str(i * 2)] + 
+								   [G.nodes[pattern[0]][node_label]] + canonlist)
+				treelet.append(canonkey_t)
+			canonkey_l.update(Counter(treelet))
+
+		# pattern 7
+		treelet = []
+		for pattern in patterns['7']:
+			canonlist = [tuple((G.nodes[leaf][node_label], 
+								G[leaf][pattern[0]][edge_label])) for leaf in pattern[1:3]]
+			canonlist.sort()
+			canonlist = list(chain.from_iterable(canonlist))
+			canonkey_t = tuple(['7'] + [G.nodes[pattern[0]][node_label]] + canonlist 
+							   + [G.nodes[pattern[3]][node_label]] 
+							   + [G[pattern[3]][pattern[0]][edge_label]]
+							   + [G.nodes[pattern[4]][node_label]] 
+							   + [G[pattern[4]][pattern[3]][edge_label]])
+			treelet.append(canonkey_t)
+		canonkey_l.update(Counter(treelet))
+
+		# pattern 11
+		treelet = []
+		for pattern in patterns['11']:
+			canonlist = [tuple((G.nodes[leaf][node_label], 
+								G[leaf][pattern[0]][edge_label])) for leaf in pattern[1:4]]
+			canonlist.sort()
+			canonlist = list(chain.from_iterable(canonlist))
+			canonkey_t = tuple(['b'] + [G.nodes[pattern[0]][node_label]] + canonlist 
+							   + [G.nodes[pattern[4]][node_label]] 
+							   + [G[pattern[4]][pattern[0]][edge_label]]
+							   + [G.nodes[pattern[5]][node_label]] 
+							   + [G[pattern[5]][pattern[4]][edge_label]])
+			treelet.append(canonkey_t)
+		canonkey_l.update(Counter(treelet))
+
+		# pattern 10
+		treelet = []
+		for pattern in patterns['10']:
+			canonkey4 = [G.nodes[pattern[5]][node_label], G[pattern[5]][pattern[4]][edge_label]]
+			canonlist = [tuple((G.nodes[leaf][node_label], 
+								G[leaf][pattern[0]][edge_label])) for leaf in pattern[1:3]]
+			canonlist.sort()
+			canonkey0 = list(chain.from_iterable(canonlist))
+			canonkey_t = tuple(['a'] + [G.nodes[pattern[3]][node_label]] 
+							   + [G.nodes[pattern[4]][node_label]] 
+							   + [G[pattern[4]][pattern[3]][edge_label]] 
+							   + [G.nodes[pattern[0]][node_label]] 
+							   + [G[pattern[0]][pattern[3]][edge_label]] 
+							   + canonkey4 + canonkey0)
+			treelet.append(canonkey_t)
+		canonkey_l.update(Counter(treelet))
+
+		# pattern 12
+		treelet = []
+		for pattern in patterns['12']:
+			canonlist0 = [tuple((G.nodes[leaf][node_label], 
+								 G[leaf][pattern[0]][edge_label])) for leaf in pattern[1:3]]
+			canonlist0.sort()
+			canonlist0 = list(chain.from_iterable(canonlist0))
+			canonlist3 = [tuple((G.nodes[leaf][node_label], 
+								 G[leaf][pattern[3]][edge_label])) for leaf in pattern[4:6]]
+			canonlist3.sort()
+			canonlist3 = list(chain.from_iterable(canonlist3))
+			
+			# 2 possible key can be generated from 2 nodes with extended label 3, 
+			# select the one with lower lexicographic order.
+			canonkey_t1 = tuple(['c'] + [G.nodes[pattern[0]][node_label]] + canonlist0 
+								+ [G.nodes[pattern[3]][node_label]] 
+								+ [G[pattern[3]][pattern[0]][edge_label]] 
+								+ canonlist3)
+			canonkey_t2 = tuple(['c'] + [G.nodes[pattern[3]][node_label]] + canonlist3 
+								+ [G.nodes[pattern[0]][node_label]] 
+								+ [G[pattern[0]][pattern[3]][edge_label]] 
+								+ canonlist0)
+			treelet.append(canonkey_t1 if canonkey_t1 < canonkey_t2 else canonkey_t2)
+		canonkey_l.update(Counter(treelet))
+
+		# pattern 9
+		treelet = []
+		for pattern in patterns['9']:
+			canonkey2 = [G.nodes[pattern[4]][node_label], G[pattern[4]][pattern[2]][edge_label]]
+			canonkey3 = [G.nodes[pattern[5]][node_label], G[pattern[5]][pattern[3]][edge_label]]
+			prekey2 = [G.nodes[pattern[2]][node_label], G[pattern[2]][pattern[0]][edge_label]]
+			prekey3 = [G.nodes[pattern[3]][node_label], G[pattern[3]][pattern[0]][edge_label]]
+			if prekey2 + canonkey2 < prekey3 + canonkey3:
+				canonkey_t = [G.nodes[pattern[1]][node_label]] \
+							 + [G[pattern[1]][pattern[0]][edge_label]] \
+							 + prekey2 + prekey3 + canonkey2 + canonkey3
+			else:
+				canonkey_t = [G.nodes[pattern[1]][node_label]] \
+							 + [G[pattern[1]][pattern[0]][edge_label]] \
+							 + prekey3 + prekey2 + canonkey3 + canonkey2
+			treelet.append(tuple(['9'] + [G.nodes[pattern[0]][node_label]] + canonkey_t))
+		canonkey_l.update(Counter(treelet))
+
+		return canonkey_l
+
+	return canonkey
+
+
+def wrapper_get_canonkeys(node_label, edge_label, labeled, is_directed, itr_item):
+	g = itr_item[0]
+	i = itr_item[1]
+	return i, get_canonkeys(g, node_label, edge_label, labeled, is_directed)
+	
+
+def find_paths(G, source_node, length):
+	"""Find all paths with a certain length those start from a source node. 
+	A recursive depth first search is applied.
+	
+	Parameters
+	----------
+	G : NetworkX graphs
+		The graph in which paths are searched.
+	source_node : integer
+		The number of the node from where all paths start.
+	length : integer
+		The length of paths.
+		
+	Return
+	------
+	path : list of list
+		List of paths retrieved, where each path is represented by a list of nodes.
+	"""
+	if length == 0:
+		return [[source_node]]
+	path = [[source_node] + path for neighbor in G[source_node] \
+		for path in find_paths(G, neighbor, length - 1) if source_node not in path]
+	return path
+
+
+def find_all_paths(G, length, is_directed):
+	"""Find all paths with a certain length in a graph. A recursive depth first
+	search is applied.
+	
+	Parameters
+	----------
+	G : NetworkX graphs
+		The graph in which paths are searched.
+	length : integer
+		The length of paths.
+		
+	Return
+	------
+	path : list of list
+		List of paths retrieved, where each path is represented by a list of nodes.
+	"""
+	all_paths = []
+	for node in G:
+		all_paths.extend(find_paths(G, node, length))
+		
+	if not is_directed:
+		# For each path, two presentations are retrieved from its two extremities. 
+		# Remove one of them.
+		all_paths_r = [path[::-1] for path in all_paths]  
+		for idx, path in enumerate(all_paths[:-1]):
+			for path2 in all_paths_r[idx+1::]:
+				if path == path2:
+					all_paths[idx] = []
+					break
+		all_paths = list(filter(lambda a: a != [], all_paths))
+			
+	return all_paths