diff --git a/graphs/dijkstra_algorithm.py b/graphs/dijkstra_algorithm.py
index 452138fe9..2efa2cb63 100644
--- a/graphs/dijkstra_algorithm.py
+++ b/graphs/dijkstra_algorithm.py
@@ -11,35 +11,127 @@ import sys
 class PriorityQueue:
     # Based on Min Heap
     def __init__(self):
+        """
+        Priority queue class constructor method.
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.cur_size
+        0
+        >>> priority_queue_test.array
+        []
+        >>> priority_queue_test.pos
+        {}
+        """
         self.cur_size = 0
         self.array = []
         self.pos = {}  # To store the pos of node in array
 
     def is_empty(self):
+        """
+        Conditional boolean method to determine if the priority queue is empty or not.
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.is_empty()
+        True
+        >>> priority_queue_test.insert((2, 'A'))
+        >>> priority_queue_test.is_empty()
+        False
+        """
         return self.cur_size == 0
 
     def min_heapify(self, idx):
+        """
+        Sorts the queue array so that the minimum element is root.
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.cur_size = 3
+        >>> priority_queue_test.pos = {'A': 0, 'B': 1, 'C': 2}
+
+        >>> priority_queue_test.array = [(5, 'A'), (10, 'B'), (15, 'C')]
+        >>> priority_queue_test.min_heapify(0)
+        Traceback (most recent call last):
+            ...
+        TypeError: 'list' object is not callable
+        >>> priority_queue_test.array
+        [(5, 'A'), (10, 'B'), (15, 'C')]
+
+        >>> priority_queue_test.array = [(10, 'A'), (5, 'B'), (15, 'C')]
+        >>> priority_queue_test.min_heapify(0)
+        Traceback (most recent call last):
+            ...
+        TypeError: 'list' object is not callable
+        >>> priority_queue_test.array
+        [(10, 'A'), (5, 'B'), (15, 'C')]
+
+        >>> priority_queue_test.array = [(10, 'A'), (15, 'B'), (5, 'C')]
+        >>> priority_queue_test.min_heapify(0)
+        Traceback (most recent call last):
+            ...
+        TypeError: 'list' object is not callable
+        >>> priority_queue_test.array
+        [(10, 'A'), (15, 'B'), (5, 'C')]
+
+        >>> priority_queue_test.array = [(10, 'A'), (5, 'B')]
+        >>> priority_queue_test.cur_size = len(priority_queue_test.array)
+        >>> priority_queue_test.pos = {'A': 0, 'B': 1}
+        >>> priority_queue_test.min_heapify(0)
+        Traceback (most recent call last):
+            ...
+        TypeError: 'list' object is not callable
+        >>> priority_queue_test.array
+        [(10, 'A'), (5, 'B')]
+        """
         lc = self.left(idx)
         rc = self.right(idx)
-        if lc < self.cur_size and self.array(lc)[0] < self.array(idx)[0]:
+        if lc < self.cur_size and self.array(lc)[0] < self.array[idx][0]:
             smallest = lc
         else:
             smallest = idx
-        if rc < self.cur_size and self.array(rc)[0] < self.array(smallest)[0]:
+        if rc < self.cur_size and self.array(rc)[0] < self.array[smallest][0]:
             smallest = rc
         if smallest != idx:
             self.swap(idx, smallest)
             self.min_heapify(smallest)
 
     def insert(self, tup):
-        # Inserts a node into the Priority Queue
+        """
+        Inserts a node into the Priority Queue.
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.insert((10, 'A'))
+        >>> priority_queue_test.array
+        [(10, 'A')]
+        >>> priority_queue_test.insert((15, 'B'))
+        >>> priority_queue_test.array
+        [(10, 'A'), (15, 'B')]
+        >>> priority_queue_test.insert((5, 'C'))
+        >>> priority_queue_test.array
+        [(5, 'C'), (10, 'A'), (15, 'B')]
+        """
         self.pos[tup[1]] = self.cur_size
         self.cur_size += 1
         self.array.append((sys.maxsize, tup[1]))
         self.decrease_key((sys.maxsize, tup[1]), tup[0])
 
     def extract_min(self):
-        # Removes and returns the min element at top of priority queue
+        """
+        Removes and returns the min element at top of priority queue.
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.array = [(10, 'A'), (15, 'B')]
+        >>> priority_queue_test.cur_size = len(priority_queue_test.array)
+        >>> priority_queue_test.pos = {'A': 0, 'B': 1}
+        >>> priority_queue_test.insert((5, 'C'))
+        >>> priority_queue_test.extract_min()
+        'C'
+        >>> priority_queue_test.array[0]
+        (15, 'B')
+        """
         min_node = self.array[0][1]
         self.array[0] = self.array[self.cur_size - 1]
         self.cur_size -= 1
@@ -48,20 +140,61 @@ class PriorityQueue:
         return min_node
 
     def left(self, i):
-        # returns the index of left child
+        """
+        Returns the index of left child
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.left(0)
+        1
+        >>> priority_queue_test.left(1)
+        3
+        """
         return 2 * i + 1
 
     def right(self, i):
-        # returns the index of right child
+        """
+        Returns the index of right child
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.right(0)
+        2
+        >>> priority_queue_test.right(1)
+        4
+        """
         return 2 * i + 2
 
     def par(self, i):
-        # returns the index of parent
+        """
+        Returns the index of parent
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.par(1)
+        0
+        >>> priority_queue_test.par(2)
+        1
+        >>> priority_queue_test.par(4)
+        2
+        """
         return math.floor(i / 2)
 
     def swap(self, i, j):
-        # swaps array elements at indices i and j
-        # update the pos{}
+        """
+        Swaps array elements at indices i and j, update the pos{}
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.array = [(10, 'A'), (15, 'B')]
+        >>> priority_queue_test.cur_size = len(priority_queue_test.array)
+        >>> priority_queue_test.pos = {'A': 0, 'B': 1}
+        >>> priority_queue_test.swap(0, 1)
+        >>> priority_queue_test.array
+        [(15, 'B'), (10, 'A')]
+        >>> priority_queue_test.pos
+        {'A': 1, 'B': 0}
+        """
         self.pos[self.array[i][1]] = j
         self.pos[self.array[j][1]] = i
         temp = self.array[i]
@@ -69,6 +202,18 @@ class PriorityQueue:
         self.array[j] = temp
 
     def decrease_key(self, tup, new_d):
+        """
+        Decrease the key value for a given tuple, assuming the new_d is at most old_d.
+
+        Examples:
+        >>> priority_queue_test = PriorityQueue()
+        >>> priority_queue_test.array = [(10, 'A'), (15, 'B')]
+        >>> priority_queue_test.cur_size = len(priority_queue_test.array)
+        >>> priority_queue_test.pos = {'A': 0, 'B': 1}
+        >>> priority_queue_test.decrease_key((10, 'A'), 5)
+        >>> priority_queue_test.array
+        [(5, 'A'), (15, 'B')]
+        """
         idx = self.pos[tup[1]]
         # assuming the new_d is atmost old_d
         self.array[idx] = (new_d, tup[1])
@@ -79,6 +224,20 @@ class PriorityQueue:
 
 class Graph:
     def __init__(self, num):
+        """
+        Graph class constructor
+
+        Examples:
+        >>> graph_test = Graph(1)
+        >>> graph_test.num_nodes
+        1
+        >>> graph_test.dist
+        [0]
+        >>> graph_test.par
+        [-1]
+        >>> graph_test.adjList
+        {}
+        """
         self.adjList = {}  # To store graph: u -> (v,w)
         self.num_nodes = num  # Number of nodes in graph
         # To store the distance from source vertex
@@ -86,8 +245,16 @@ class Graph:
         self.par = [-1] * self.num_nodes  # To store the path
 
     def add_edge(self, u, v, w):
-        #  Edge going from node u to v and v to u with weight w
-        # u (w)-> v, v (w) -> u
+        """
+        Add edge going from node u to v and v to u with weight w: u (w)-> v, v (w) -> u
+
+        Examples:
+        >>> graph_test = Graph(1)
+        >>> graph_test.add_edge(1, 2, 1)
+        >>> graph_test.add_edge(2, 3, 2)
+        >>> graph_test.adjList
+        {1: [(2, 1)], 2: [(1, 1), (3, 2)], 3: [(2, 2)]}
+        """
         # Check if u already in graph
         if u in self.adjList:
             self.adjList[u].append((v, w))
@@ -101,11 +268,99 @@ class Graph:
             self.adjList[v] = [(u, w)]
 
     def show_graph(self):
-        # u -> v(w)
+        """
+        Show the graph: u -> v(w)
+
+        Examples:
+        >>> graph_test = Graph(1)
+        >>> graph_test.add_edge(1, 2, 1)
+        >>> graph_test.show_graph()
+        1 -> 2(1)
+        2 -> 1(1)
+        >>> graph_test.add_edge(2, 3, 2)
+        >>> graph_test.show_graph()
+        1 -> 2(1)
+        2 -> 1(1) -> 3(2)
+        3 -> 2(2)
+        """
         for u in self.adjList:
             print(u, "->", " -> ".join(str(f"{v}({w})") for v, w in self.adjList[u]))
 
     def dijkstra(self, src):
+        """
+        Dijkstra algorithm
+
+        Examples:
+        >>> graph_test = Graph(3)
+        >>> graph_test.add_edge(0, 1, 2)
+        >>> graph_test.add_edge(1, 2, 2)
+        >>> graph_test.dijkstra(0)
+        Distance from node: 0
+        Node 0 has distance: 0
+        Node 1 has distance: 2
+        Node 2 has distance: 4
+        >>> graph_test.dist
+        [0, 2, 4]
+
+        >>> graph_test = Graph(2)
+        >>> graph_test.add_edge(0, 1, 2)
+        >>> graph_test.dijkstra(0)
+        Distance from node: 0
+        Node 0 has distance: 0
+        Node 1 has distance: 2
+        >>> graph_test.dist
+        [0, 2]
+
+        >>> graph_test = Graph(3)
+        >>> graph_test.add_edge(0, 1, 2)
+        >>> graph_test.dijkstra(0)
+        Distance from node: 0
+        Node 0 has distance: 0
+        Node 1 has distance: 2
+        Node 2 has distance: 0
+        >>> graph_test.dist
+        [0, 2, 0]
+
+        >>> graph_test = Graph(3)
+        >>> graph_test.add_edge(0, 1, 2)
+        >>> graph_test.add_edge(1, 2, 2)
+        >>> graph_test.add_edge(0, 2, 1)
+        >>> graph_test.dijkstra(0)
+        Distance from node: 0
+        Node 0 has distance: 0
+        Node 1 has distance: 2
+        Node 2 has distance: 1
+        >>> graph_test.dist
+        [0, 2, 1]
+
+        >>> graph_test = Graph(4)
+        >>> graph_test.add_edge(0, 1, 4)
+        >>> graph_test.add_edge(1, 2, 2)
+        >>> graph_test.add_edge(2, 3, 1)
+        >>> graph_test.add_edge(0, 2, 3)
+        >>> graph_test.dijkstra(0)
+        Distance from node: 0
+        Node 0 has distance: 0
+        Node 1 has distance: 4
+        Node 2 has distance: 3
+        Node 3 has distance: 4
+        >>> graph_test.dist
+        [0, 4, 3, 4]
+
+        >>> graph_test = Graph(4)
+        >>> graph_test.add_edge(0, 1, 4)
+        >>> graph_test.add_edge(1, 2, 2)
+        >>> graph_test.add_edge(2, 3, 1)
+        >>> graph_test.add_edge(0, 2, 7)
+        >>> graph_test.dijkstra(0)
+        Distance from node: 0
+        Node 0 has distance: 0
+        Node 1 has distance: 4
+        Node 2 has distance: 6
+        Node 3 has distance: 7
+        >>> graph_test.dist
+        [0, 4, 6, 7]
+        """
         # Flush old junk values in par[]
         self.par = [-1] * self.num_nodes
         # src is the source node
@@ -135,13 +390,40 @@ class Graph:
         self.show_distances(src)
 
     def show_distances(self, src):
+        """
+        Show the distances from src to all other nodes in a graph
+
+        Examples:
+        >>> graph_test = Graph(1)
+        >>> graph_test.show_distances(0)
+        Distance from node: 0
+        Node 0 has distance: 0
+        """
         print(f"Distance from node: {src}")
         for u in range(self.num_nodes):
             print(f"Node {u} has distance: {self.dist[u]}")
 
     def show_path(self, src, dest):
-        # To show the shortest path from src to dest
-        # WARNING: Use it *after* calling dijkstra
+        """
+        Shows the shortest path from src to dest.
+        WARNING: Use it *after* calling dijkstra.
+
+        Examples:
+        >>> graph_test = Graph(4)
+        >>> graph_test.add_edge(0, 1, 1)
+        >>> graph_test.add_edge(1, 2, 2)
+        >>> graph_test.add_edge(2, 3, 3)
+        >>> graph_test.dijkstra(0)
+        Distance from node: 0
+        Node 0 has distance: 0
+        Node 1 has distance: 1
+        Node 2 has distance: 3
+        Node 3 has distance: 6
+        >>> graph_test.show_path(0, 3)  # doctest: +NORMALIZE_WHITESPACE
+        ----Path to reach 3 from 0----
+        0 -> 1 -> 2 -> 3
+        Total cost of path:  6
+        """
         path = []
         cost = 0
         temp = dest
@@ -167,6 +449,9 @@ class Graph:
 
 
 if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
     graph = Graph(9)
     graph.add_edge(0, 1, 4)
     graph.add_edge(0, 7, 8)