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gistfile1.txt

"""
@author : saimadhav heblikar
usage: python compr.py [-c | -d] <input file> <output file>
Call -c for compress
Call -d for decompress
Make sure to escape the input file and output with with double quotes if you
are on a NT System!!!

Purpose:Given a input file,a compressed output file is generated along with the
overhead required to decompress it.

"""
import heapq
from sys import argv

class node():

    def __init__(self,char,freq,left_child,right_child,parent):
        self.char=char
        self.freq=freq
        self.left_child=left_child
        self.right_child=right_child
        self.parent=parent


def extract_code(root):
    global d
    if root != None:
        extract_code(root[1].left_child)
        if root[1].right_child==None and root[1].left_child==None:
            s=""
            child=root[1]
            parent=child.parent
            while(parent!=None):

                if(child==parent.left_child[1]):
                    s='0'+s
                else:
                    s='1'+s
                child=parent
                parent=parent.parent
            d[root[1].char]=s
        extract_code(root[1].right_child)

def compress(msg):
    #Create freq dict
    global d
    for i in msg:
        if i in d:
            d[i]=d[i]+1
        else:
            d[i]=1
    queue=[]
    for char,freq in d.iteritems():
        temp_node=node(char,freq,None,None,None)
        heapq.heappush(queue,(freq,temp_node))
    while len(queue)>1:
        temp_node1=heapq.heappop(queue)
        temp_node2=heapq.heappop(queue)
        new_node=node('*',temp_node1[0]+temp_node2[0],temp_node1,temp_node2,None)
        temp_node1[1].parent=new_node
        temp_node2[1].parent=new_node
        heapq.heappush(queue,(new_node.freq,new_node))

    #print queue[0]
    queue[0][1].left_child,queue[0][1].right_child=queue[0][1].right_child,queue[0][1].left_child
    d={}
    extract_code(queue[0])
    compressed_msg=''
    for i in msg:
        compressed_msg=compressed_msg+d[i]
    return compressed_msg

def decompress():
    pass
    #todo
d={}
msg=argv[2]
print msg
c=compress(msg)
print c
print 'msg size in bytes:'+str(len(msg))
print 'compressed msg size in bytes:'+str(len(c)/8) #BIT ARRAY LENGTH