Python Linked List: Insert an item in front of a given doubly linked list
Python Linked List: Exercise-12 with Solution
Write a Python program to insert an item in front of a given doubly linked list.
Sample Solution:-
Python Code:
class Node(object):
# Singly linked node
def __init__(self, data=None, next=None, prev=None):
self.data = data
self.next = next
self.prev = prev
class doubly_linked_list(object):
def __init__(self):
self.head = None
self.tail = None
self.count = 0
def append_item(self, data):
# Append an item
new_item = Node(data, None, None)
if self.head is None:
self.head = new_item
self.tail = self.head
else:
new_item.prev = self.tail
self.tail.next = new_item
self.tail = new_item
self.count += 1
def iter(self):
# Iterate the list
current = self.head
while current:
item_val = current.data
current = current.next
yield item_val
def print_foward(self):
for node in self.iter():
print(node)
def insert_start(self, data):
if self.head is not None:
new_node = Node(data, None, None)
new_node.next = self.head
self.head.prev = new_node
self.head = new_node
self.count += 1
items = doubly_linked_list()
items.append_item('PHP')
items.append_item('Python')
items.append_item('C#')
items.append_item('C++')
items.append_item('Java')
items.append_item('SQL')
print("Original list:")
items.print_foward()
print("\nAppend item in front of the list:")
items.insert_start("Perl")
items.print_foward()
Sample Output:
Original list: PHP Python C# C++ Java SQL Append item in front of the list: Perl PHP Python C# C++ Java SQL
Flowchart:
Python Code Editor:
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Previous: Write a Python program to print a given doubly linked list in reverse order.
Next: Write a Python program to search a specific item in a given doubly linked list and return true if the item is found otherwise return false.
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Python: Tips of the Day
Find current directory and file's directory:
To get the full path to the directory a Python file is contained in, write this in that file:
import os dir_path = os.path.dirname(os.path.realpath(__file__))
(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)
To get the current working directory use
import os cwd = os.getcwd()
Documentation references for the modules, constants and functions used above:
- The os and os.path modules.
- The __file__ constant
- os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
- os.path.dirname(path) (returns "the directory name of pathname path")
- os.getcwd() (returns "a string representing the current working directory")
- os.chdir(path) ("change the current working directory to path")
Ref: https://bit.ly/3fy0R6m
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