structures.py

# study some high-level data structures in python
# ref: http://blog.jobbole.com/65218/

import collections as cl
import array
import heapq
import bisect
import weakref
import pprint


### collections

# Counter
# count the number of times an element occurs
def test_counter():
 li = ["Dog", "Cat", "Mouse", 42, "Dog", 42, "Cat", "Dog"]
 a = cl.Counter(li)
 print a
 print a.most_common(2)


# Deque
def test_deque():
 q = cl.deque(range(5))
 print q
 q.append(13)
 q.appendleft(22)
 print q
 print q.pop()
 print q.popleft()
 print q
 q.rotate(2)
 print q

# Defaultdict
# Same with dict, except when a key not exists
def test_defaultdict():
 s = "the quick brown fox jumps over the lazy dog"
 words = s.split()
 l = cl.defaultdict(list)
 for k,v in enumerate(words):
 l[v].append(k)
 print l

 d = {}
 for k,v in enumerate(words):
 d.setdefault(k,[]).append(v)
 print d

 # same with counter
 li = ["Dog", "Cat", "Mouse", 42, "Dog", 42, "Cat", "Dog"]
 dd = cl.defaultdict(int)
 for k in li:
 dd[k] += 1
 print dd


### Array: small than list, element with one type

# i is type code, stands for signed int
def test_array():
 a = array.array('i',range(5))
 print a
 b = array.array(a.typecode,[x*2 for x in a])
 print b
 for i,x in enumerate(a):
 a[i] = x*2
 print a

### heapq

def test_heapq():
 heap = []
 for v in range(5):
 heapq.heappush(heap,v)
 print heapq.heappop(heap)
 print heapq.nlargest(3,heap)

### bisect
def test_bisect():
 a = [1,2,6,89]
 bisect.insort_right(a,4)
 print a
 print bisect.bisect(a,3)

### weakref
# like = , strong ref. except destroyed only when none ref is left
# do not really understand yet!
def test_weakref():
 a = 2
 b = a
 del b
 print a
 
 class Foo():
 a = 1
 f = Foo()
 d = weakref.ref(f)
 del f
 print d

### pprint
# beautiful print
def test_pprint():
 matrix = [ [1,2,3], [4,5,6], [7,8,9] ]
 a = pprint.PrettyPrinter(width = 20)
 a.pprint(matrix)

if __name__ == '__main__':
# test_counter()
# test_deque()
# test_defaultdict()
# test_array()
# test_heapq()
# test_bisect()
# test_weakref()
 test_pprint()