Improved on Singly Linked List Programs (#1558)

* Improved Singly Linked List
Added String Representations of Nodes and Linked Lists
Added support for indexing and changing of Node data using indices.

* Added a few comments to Linked Lists

* Reformatted to conform to PEP8

* Added from_sequence.py
Convert a Python List to Linked List comprising of Nodes and return head.

* Added print_reverse.py
Recursive program to print the elements of a Linked List in reverse.

* Change 'is not None' for more Pythonicness

data_structures/linked_list/from_sequence.py

@@ -0,0 +1,45 @@
+# Recursive Prorgam to create a Linked List from a sequence and
+# print a string representation of it.
+
+class Node:
+    def __init__(self, data=None):
+        self.data = data
+        self.next = None
+
+    def __repr__(self):
+        """Returns a visual representation of the node and all its following nodes."""
+        string_rep = ""
+        temp = self
+        while temp:
+            string_rep += f"<{temp.data}> ---> "
+            temp = temp.next
+        string_rep += "<END>"
+        return string_rep
+
+
+
+def make_linked_list(elements_list):
+    """Creates a Linked List from the elements of the given sequence
+    (list/tuple) and returns the head of the Linked List."""
+
+    # if elements_list is empty
+    if not elements_list:
+        raise Exception("The Elements List is empty")
+
+    # Set first element as Head
+    head = Node(elements_list[0])
+    current = head
+    # Loop through elements from position 1
+    for data in elements_list[1:]:
+        current.next = Node(data)
+        current = current.next
+    return head
+
+
+
+list_data = [1,3,5,32,44,12,43]
+print(f"List: {list_data}")
+print("Creating Linked List from List.")
+linked_list = make_linked_list(list_data)
+print("Linked List:")
+print(linked_list)