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Exercise_5.py
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Exercise_5.py
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import os
import math
import heapq
import operator
from bitarray import bitarray
END_CONTENT_CHAR = '$'
class Node:
def __init__(self, char, freq):
self.char = char
self.freq = freq
self.left = None
self.right = None
def __eq__(self, other):
return self.freq == other.freq
def __lt__(self, other):
return self.freq < other.freq
def __gt__(self, other):
return self.freq > other.freq
# Read file - return content
def read_file(file_name):
file = open(file_name, 'r')
return file.read()
# Analyze content - calculate probability
def analyze_content(content):
letters = {}
counter = 0
for _, letter in enumerate(content):
cardinality = letters.get(letter, 0)
letters.update({letter: cardinality + 1})
counter += 1
return letters, counter
# Order letters dictionary - top used as first
def order_dictionary(dictionary):
return dict(sorted(dictionary.items(), key=operator.itemgetter(1), reverse=True))
# Make heap of nodes
def make_nodes_heap(dictionary):
heap = []
for (key, value) in dictionary.items():
node = Node(key, value)
heapq.heappush(heap, node)
return heap
# Merge nodes to prepare binary tree
def merge_nodes(heap):
while len(heap) > 1:
node1 = heapq.heappop(heap)
node2 = heapq.heappop(heap)
merged = Node(None, node1.freq + node2.freq)
merged.left = node1
merged.right = node2
heapq.heappush(heap, merged)
return heap
# Code helper to prepare dictionary with codes and characters
def code_helper(root, current_code, codes):
# Return when None
if not root:
return
# Required assign character to node (only leaf has)
if root.char:
codes[root.char] = current_code
return
# Recursion
code_helper(root.left, current_code + '0', codes)
code_helper(root.right, current_code + '1', codes)
# Prepare codes
def make_codes(heap):
current_code = ''
codes = {}
root = heapq.heappop(heap)
code_helper(root, current_code, codes)
return codes
# Create code
def create(dictionary):
nodes = make_nodes_heap(dictionary)
heap = merge_nodes(nodes)
codes = make_codes(heap)
return codes
# Encode text
def encode(code_dict, text):
code = []
for letter in text:
code.append(code_dict.get(letter))
# Append end of stream
code.append(code_dict.get(END_CONTENT_CHAR))
return bitarray(''.join(code))
# Simple cast char to bits
def string2bits(s):
return [bin(ord(x))[2:].zfill(8) for x in s]
# Save encoded details to file
def save(code_dict, encoded_content, directory):
if not os.path.exists(directory):
os.makedirs(directory)
with open(directory + 'encoded_result.bin', 'wb') as content_file:
encoded_content.tofile(content_file)
with open(directory + 'key.bin', 'wb') as key_file:
code_bits = []
for (key, value) in code_dict.items():
for x in string2bits(key):
code_bits.append(x)
for x in string2bits(str(len(value))):
code_bits.append(x)
for x in string2bits(':'):
code_bits.append(x)
code_bits.append(value)
key_file.write(bitarray(''.join(code_bits)).tobytes())
# Load content from file
def load(directory):
encoded_content = bitarray()
encoded_key = bitarray()
code = {}
with open(directory + 'encoded_result.bin', 'rb') as content_file:
encoded_content.fromfile(content_file)
with open(directory + 'key.bin', 'rb') as key_file:
encoded_key.fromfile(key_file)
total_length = encoded_key.length()
length = 0
while length < total_length:
key = encoded_key[length: length + 8].tostring()
length += 8
size = []
temp = '0'
while temp != ':' and temp != '':
size.append(temp)
temp = encoded_key[length: length + 8].tostring()
length += 8
code_length = int(''.join(size))
code_bits = encoded_key[length: length + code_length].to01()
length += code_length
code[code_bits] = key
return encoded_content, code
# Decode already encoded text
def decode(encoded_bits, code_dict):
decoded = ''
current_code = ''
for bit in encoded_bits.to01():
current_code += str(bit)
if current_code in code_dict:
char = code_dict.get(current_code)
if char != END_CONTENT_CHAR:
decoded += char
current_code = ''
else:
return decoded
return decoded
# Calculate size
def calculate_sizes(directory, original):
encoded_size = os.stat(directory + 'encoded_result.bin').st_size
key_size = os.stat(directory + 'key.bin').st_size
original_size = os.stat(original).st_size
return encoded_size, key_size, original_size
def entropy(dictionary):
# Entropy sum
entropy_result = 0.0
# Loop to analyze
for key, value in dictionary.items():
entropy_result += value * math.log(value, 2)
# Return result
return -entropy_result
def to_probability(dictionary, counter):
for letter in dictionary:
dictionary.update({letter: dictionary.get(letter) / counter})
return dictionary
# Main function
def main():
directory = 'encoded/'
file_name = 'norm_wiki_sample.txt'
content = read_file(file_name)
letters_dictionary, counter = analyze_content(content)
counter += 1
letters_dictionary.update({END_CONTENT_CHAR: 1})
ordered_dictionary = order_dictionary(letters_dictionary)
code = create(ordered_dictionary)
encoded = encode(code, content)
save(code, encoded, directory)
encoded_content, enc_code = load(directory)
decoded = decode(encoded_content, enc_code)
en_size, k_size, o_size = calculate_sizes(directory, file_name)
sum_size = k_size + en_size
sd = encoded.length() / len(content)
ce = entropy(to_probability(letters_dictionary, counter)) / sd
print('Original file => ' + file_name)
print('Size => ' + str(o_size) + ' [bytes]')
print('Encoded size:')
print('\tEncoded => ' + str(en_size) + ' [bytes]')
print('\tKey => ' + str(k_size) + ' [bytes]')
print('\tSUM => ' + str(sum_size) + ' [bytes]')
print('\tSD => ' + str(sd))
print('\tCE => ' + str(ce))
print('Compare files')
if decoded == content:
print('\tEquality correct ✓')
print('\tCompression Ratio => ' + str(o_size / sum_size))
print('\tSpace savings => ' + str(1 - sum_size / o_size))
else:
print('\tContent =/= Decoded(Encoded(Content))')
print(content)
print('\n\n--------\n\n')
print(decoded)
if __name__ == '__main__':
main()