def build_codec(freq_list):
"""
Purpose:
Build a dictionary containing character:code pairs from the frequency list.
Pre-conditions:
:param freq_list: A list of (frequency,character) pairs.
Return:
:return: a dictionary
"""
def get_frequency(a_HuffmanTree):
"""
helper function for sorting the list according to frequency of the char
:param a_HuffmanTree:
:return:
"""
return a_HuffmanTree.get_freq()
leafs = [HT.HuffmanTree(freq=f, char=c) for c,f in freq_list]
leafs.sort(key=get_frequency)
heap = HP.HuffmanHeap(leafs, [])
while len(heap.old) != 0:
temp1 = heap.dequeue()
temp2 = heap.dequeue()
item3 = HT.HuffmanTree(temp1.get_freq()+temp2.get_freq(),left=temp1,right=temp2)
heap.enqueue(item3)
if len(heap.new) >= 2:
while True:
temp1 = heap.dequeue()
temp2 = heap.dequeue()
item3 = HT.HuffmanTree(temp1.get_freq() + temp2.get_freq(), left=temp1, right=temp2)
if len(heap.new) == 0:
heap.enqueue(item3)
break
heap.enqueue(item3)
return heap.new[0].build_codec()
def build_codec(freq_list):
"""
Purpose:
Build a dictionary containing character:code pairs from
the frequency list.
Pre-conditions:
:param freq_list: A list of (character,frequency) pairs.
Return:
:return: a dictionary
"""
# sort the frequency list
freq_list.sort(key=lambda p: p[1])
# create the queue of Huffman trees
# note: a new ADT for this purpose!
hq = HH.HuffmanHeap([HT.HuffmanTree(freq=f, char=c) for c, f in freq_list])
# dequeue 2 trees, combine them, and enqueue the resulting tree
while len(hq) > 1:
t1 = hq.dequeue()
t2 = hq.dequeue()
hq.enqueue(HT.HuffmanTree(left=t1, right=t2))
#build a codec from the only tree that's left
survivor = hq.dequeue()
return survivor.build_codec()
