import collections
students = ['Zhang San', 'Li Si', 'Zhou liu', 'Chen qi', 'Cheng ba']
# using defaultdict
dd = collections.defaultdict(list)
for s in students:
	key = s[0]
	dd[key].append(s)
print(dd)
# using original dict (method 1)
od = {}
for s in students:
	key = s[0]
	if key not in do:
		od[key] = []
	od[key].append(s)
print(od)

scores = ['A', 'B', 'C', 'A', 'A', 'B', 'C', 'B', 'A', 'A']
# using defaultdict
dd = collections.defaultdict(int)
for s in scores :
	dd[s] += 1
print(dd)
# using original dict (method 2)
od = collections.defaultdict(int)
for s in scores :
	if s not in do:
		do[s] = 1
	else:
		do[s] += 1
print(od)

# class
class Rect:
	def __init__(self, x1, y1, x2, y2):
		self.x1 = x1
		self.y1 = y1
		self.x2 = x2
		self.y2 = y2
		
def area_class(r):
	w = r.x2 - r.x1
	h = r.y2 - r.y1
	return w*h

r1 = Rect(1,3,5,5)
# __main__.Rect object at 0x7fde252a87f0>
# to show its content, we need to implement __repr__(self) or __str__(self)
print(area_class(r1))

# tuple
def area_tuple(r):
	w = r[2]-r[0]
	h = r[3]-r[1]
	return w*h

r2 = (1,3,5,5)
print(r2)
# (1, 3, 5, 5)
print(area_tuple(r2))

# dict
def area_dict(r):
	w = r["x2"] - r["x1"]
	h = r["y2"] - r["y1"]
	return w*h

r3 = {"x1":1, "y1":3, "x2":5, "y2":5}
print(r3)
# {'x1': 1, 'y1': 3, 'x2': 5, 'y2': 5}
print(area_tuple(r3))

# named tuple
import collections
Rectangle = collections.namedtuple("Rectangle", ["x1", "y1", "x2", "y2"])

def area_namedtuple(r):
	w = r.x2 - r.x1
	y = r.y2 - r.y1
	return w*h

r4 = Rectangle(1,3,5,5)
print(r4)
# Rectangle(x1=1, y1=3, x2=5, y2=5)
x1,y2,x2,y2 = r4
print(x1,y2,x2,y2)
# 1 3 5 5
print(area_namedtuple(r4))
print(area_class(r4)) # work with "." grammar
print(area_tuple(r4)) # work with index
print(area_dict(r4._asdict())) # work with dict

c = Counter()                           # a new, empty counter
c = Counter('gallahad')                 # a new counter from an iterable
print(c)
# Counter({'a': 3, 'l': 2, 'g': 1, 'h': 1, 'd': 1})
c = Counter({'red': 4, 'blue': 2})      # a new counter from a mapping
print(c)
# Counter({'red': 4, 'blue': 2})
c = Counter(cats=4, dogs=8)             # a new counter from keyword args
print(c)
# Counter({'dogs': 8, 'cats': 4})

c = Counter(a=4, b=2, c=0, d=-2)
sorted(c.elements())
# ['a', 'a', 'a', 'a', 'b', 'b']
Counter('abracadabra').most_common(3)
# [('a', 5), ('b', 2), ('r', 2)]

c1 = Counter(a=4, b=2, d=-2)
c2 = Counter(a=1, b=2, c=3, d=4)
c1.subtract(c2)
c1
# Counter({'a': 3, 'b': 0, 'c': -3, 'd': -6})