diff --git a/compression/burrows_wheeler.py b/compression/burrows_wheeler.py
index 7d705af74..4ad99a642 100644
--- a/compression/burrows_wheeler.py
+++ b/compression/burrows_wheeler.py
@@ -12,6 +12,13 @@ of text compression algorithms, costing only some extra computation.
 """
 from __future__ import annotations
 
+from typing import TypedDict
+
+
+class BWTTransformDict(TypedDict):
+    bwt_string: str
+    idx_original_string: int
+
 
 def all_rotations(s: str) -> list[str]:
     """
@@ -43,7 +50,7 @@ def all_rotations(s: str) -> list[str]:
     return [s[i:] + s[:i] for i in range(len(s))]
 
 
-def bwt_transform(s: str) -> dict:
+def bwt_transform(s: str) -> BWTTransformDict:
     """
     :param s: The string that will be used at bwt algorithm
     :return: the string composed of the last char of each row of the ordered
@@ -75,10 +82,11 @@ def bwt_transform(s: str) -> dict:
     rotations = all_rotations(s)
     rotations.sort()  # sort the list of rotations in alphabetically order
     # make a string composed of the last char of each rotation
-    return {
+    response: BWTTransformDict = {
         "bwt_string": "".join([word[-1] for word in rotations]),
         "idx_original_string": rotations.index(s),
     }
+    return response
 
 
 def reverse_bwt(bwt_string: str, idx_original_string: int) -> str:
diff --git a/compression/huffman.py b/compression/huffman.py
index 8f37a53ce..d5d78b753 100644
--- a/compression/huffman.py
+++ b/compression/huffman.py
@@ -1,29 +1,31 @@
+from __future__ import annotations
+
 import sys
 
 
 class Letter:
-    def __init__(self, letter, freq):
-        self.letter = letter
-        self.freq = freq
-        self.bitstring = {}
+    def __init__(self, letter: str, freq: int):
+        self.letter: str = letter
+        self.freq: int = freq
+        self.bitstring: dict[str, str] = {}
 
-    def __repr__(self):
+    def __repr__(self) -> str:
         return f"{self.letter}:{self.freq}"
 
 
 class TreeNode:
-    def __init__(self, freq, left, right):
-        self.freq = freq
-        self.left = left
-        self.right = right
+    def __init__(self, freq: int, left: Letter | TreeNode, right: Letter | TreeNode):
+        self.freq: int = freq
+        self.left: Letter | TreeNode = left
+        self.right: Letter | TreeNode = right
 
 
-def parse_file(file_path):
+def parse_file(file_path: str) -> list[Letter]:
     """
     Read the file and build a dict of all letters and their
     frequencies, then convert the dict into a list of Letters.
     """
-    chars = {}
+    chars: dict[str, int] = {}
     with open(file_path) as f:
         while True:
             c = f.read(1)
@@ -33,22 +35,23 @@ def parse_file(file_path):
     return sorted((Letter(c, f) for c, f in chars.items()), key=lambda l: l.freq)
 
 
-def build_tree(letters):
+def build_tree(letters: list[Letter]) -> Letter | TreeNode:
     """
     Run through the list of Letters and build the min heap
     for the Huffman Tree.
     """
-    while len(letters) > 1:
-        left = letters.pop(0)
-        right = letters.pop(0)
+    response: list[Letter | TreeNode] = letters  # type: ignore
+    while len(response) > 1:
+        left = response.pop(0)
+        right = response.pop(0)
         total_freq = left.freq + right.freq
         node = TreeNode(total_freq, left, right)
-        letters.append(node)
-        letters.sort(key=lambda l: l.freq)
-    return letters[0]
+        response.append(node)
+        response.sort(key=lambda l: l.freq)
+    return response[0]
 
 
-def traverse_tree(root, bitstring):
+def traverse_tree(root: Letter | TreeNode, bitstring: str) -> list[Letter]:
     """
     Recursively traverse the Huffman Tree to set each
     Letter's bitstring dictionary, and return the list of Letters
@@ -56,13 +59,14 @@ def traverse_tree(root, bitstring):
     if type(root) is Letter:
         root.bitstring[root.letter] = bitstring
         return [root]
+    treenode: TreeNode = root  # type: ignore
     letters = []
-    letters += traverse_tree(root.left, bitstring + "0")
-    letters += traverse_tree(root.right, bitstring + "1")
+    letters += traverse_tree(treenode.left, bitstring + "0")
+    letters += traverse_tree(treenode.right, bitstring + "1")
     return letters
 
 
-def huffman(file_path):
+def huffman(file_path: str) -> None:
     """
     Parse the file, build the tree, then run through the file
     again, using the letters dictionary to find and print out the
diff --git a/compression/lempel_ziv.py b/compression/lempel_ziv.py
index 6743dc42d..ea6f33944 100644
--- a/compression/lempel_ziv.py
+++ b/compression/lempel_ziv.py
@@ -26,7 +26,7 @@ def read_file_binary(file_path: str) -> str:
 
 
 def add_key_to_lexicon(
-    lexicon: dict, curr_string: str, index: int, last_match_id: str
+    lexicon: dict[str, str], curr_string: str, index: int, last_match_id: str
 ) -> None:
     """
     Adds new strings (curr_string + "0",  curr_string + "1") to the lexicon
@@ -110,7 +110,7 @@ def write_file_binary(file_path: str, to_write: str) -> None:
         sys.exit()
 
 
-def compress(source_path, destination_path: str) -> None:
+def compress(source_path: str, destination_path: str) -> None:
     """
     Reads source file, compresses it and writes the compressed result in destination
     file
diff --git a/compression/peak_signal_to_noise_ratio.py b/compression/peak_signal_to_noise_ratio.py
index 6c6c4c38a..dded2a712 100644
--- a/compression/peak_signal_to_noise_ratio.py
+++ b/compression/peak_signal_to_noise_ratio.py
@@ -12,7 +12,7 @@ import cv2
 import numpy as np
 
 
-def psnr(original, contrast):
+def psnr(original: float, contrast: float) -> float:
     mse = np.mean((original - contrast) ** 2)
     if mse == 0:
         return 100
@@ -21,7 +21,7 @@ def psnr(original, contrast):
     return PSNR
 
 
-def main():
+def main() -> None:
     dir_path = os.path.dirname(os.path.realpath(__file__))
     # Loading images (original image and compressed image)
     original = cv2.imread(os.path.join(dir_path, "image_data/original_image.png"))