From e9d84e5de3470dd8d449e4bcdda16fd090302d17 Mon Sep 17 00:00:00 2001
From: Bahram Aghaei <aghaee.bahram@gmail.com>
Date: Thu, 11 Apr 2019 14:56:37 +0430
Subject: [PATCH] make it better

---
 Chapter1/trivial_compression.py | 81 ++++++++++++++-------------------
 1 file changed, 33 insertions(+), 48 deletions(-)

diff --git a/Chapter1/trivial_compression.py b/Chapter1/trivial_compression.py
index 3cf2a9f..0735955 100644
--- a/Chapter1/trivial_compression.py
+++ b/Chapter1/trivial_compression.py
@@ -1,54 +1,39 @@
 # trivial_compression.py
-# From Classic Computer Science Problems in Python Chapter 1
-# Copyright 2018 David Kopec
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-# http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-
 class CompressedGene:
-    def __init__(self, gene: str) -> None:
-        self._compress(gene)
+    MAP = {
+        'A': 0b00,
+        'C': 0b01,
+        'G': 0b10,
+        'T': 0b11,
+    }
+    def __init__(self, gene):
+        self.gene = gene
+        self.compres()
 
-    def _compress(self, gene: str) -> None:
-        self.bit_string: int = 1  # start with sentinel
-        for nucleotide in gene.upper():
-            self.bit_string <<= 2  # shift left two bits
-            if nucleotide == "A":  # change last two bits to 00
-                self.bit_string |= 0b00
-            elif nucleotide == "C":  # change last two bits to 01
-                self.bit_string |= 0b01
-            elif nucleotide == "G":  # change last two bits to 10
-                self.bit_string |= 0b10
-            elif nucleotide == "T":  # change last two bits to 11
-                self.bit_string |= 0b11
-            else:
-                raise ValueError("Invalid Nucleotide:{}".format(nucleotide))
+    def compres(self):
+        self.bit_string = 1
+        for n in self.gene.upper():
+            self.bit_string <<= 2
+            self.bit_string |= self.MAP[n]
 
-    def decompress(self) -> str:
-        gene: str = ""
-        for i in range(0, self.bit_string.bit_length() - 1, 2):  # - 1 to exclude sentinel
-            bits: int = self.bit_string >> i & 0b11  # get just 2 relevant bits
-            if bits == 0b00:  # A
-                gene += "A"
-            elif bits == 0b01:  # C
-                gene += "C"
-            elif bits == 0b10:  # G
-                gene += "G"
-            elif bits == 0b11:  # T
-                gene += "T"
-            else:
-                raise ValueError("Invalid bits:{}".format(bits))
-        return gene[::-1]  # [::-1] reverses string by slicing backwards
+    def decompress(self):
+        """
+        At the end of compress method, we would save an integer number
+        in self.bit_string. There is this 'bin' function in python, by which you could pass
+        an integer number and it would return the binary representation of that number, like:
+        bin(12)
+        >>'0b1100'
+        So, we could solve the decompress by using this function, just skip the
+        first 3 characters
+        string = bin(self.bit_string)[3:]
+        now, we can split the string by two characters and each group represents a nucleotide.
+        """
+        reverse_map = {v: k for k, v in self.MAP.items()}
+        gene = ''
+        for i in range(0, self.bit_string.bit_length() -1, 2):
+            bits = self.bit_string >> i & 0b11
+            gene += reverse_map[bits]
+        return gene[::-1]
 
     def __str__(self) -> str:  # string representation for pretty printing
         return self.decompress()
@@ -61,4 +46,4 @@ def __str__(self) -> str:  # string representation for pretty printing
     compressed: CompressedGene = CompressedGene(original)  # compress
     print("compressed is {} bytes".format(getsizeof(compressed.bit_string)))
     print(compressed)  # decompress
-    print("original and decompressed are the same: {}".format(original == compressed.decompress()))
\ No newline at end of file
+    print("original and decompressed are the same: {}".format(original == compressed.decompress()))