example_008_linked_list.py

''' Example of a LinkedList implementation.'''

class Link():
    ''' This class represents a link between data items only.'''
    def __init__ (self, data, next_link = None):
        self.data = data
        self.next = next_link

    def print_data(self):
        ''' Print the data contained in this link.'''
        print(self.data)

    def __str__(self):
        return str(self.data) + " --> " + str(self.next)


class LinkedList():
    ''' This class implements the operations of a simple linked list.'''
    def __init__ (self):
        self.first = None

    def insert_first (self, data):
        '''Insert data at begining of a linked list.'''
        new_link = Link(data)
        new_link.next = self.first
        self.first = new_link

    def insert_last (self, data):
        '''Insert the data at the end of a linked list.'''
        new_link = Link(data)
        current = self.first

        if current is None:
            self.first = new_link
            return
        # Find the last and insert it there.
        while current.next is not None:
            current = current.next

        current.next = new_link

    def find_link(self, data):
        '''Find to which data is the link of a given data inside this linked list.'''
        current = self.first
        if current is None:
            return None

        # Search and find the position of the given data, the get the link if.
        while current.data != data:
            if current.next is None:
                return None

            current = current.next

        return current

    def delete_link(self, data):
        '''Removes the data from the list if exist and fix the link problems.'''

        current = self.first
        previous = self.first

        if current is None:
            return None

        while current.data != data:
            if current.next is None:
                return None

            previous = current

            current = current.next

        if current == self.first:
            self.first = self.first.next
        else:
            previous.next = current.next

        return current

    def __str__(self):
        return str(self.first)


#####################################
#                                   #
#   Example run of a Linked List    #
#                                   #
#####################################
def main():
    '''A main function to demonstrate the linked list functions.'''

    my_list = LinkedList()


    my_list.insert_first(10)
    print(my_list)


    my_list.insert_first(20)
    print(my_list)


    my_list.insert_first(30)
    print(my_list)


    my_list.insert_last(1)
    print(my_list)


    print("Find Link of 10 : It is  ", my_list.find_link(10))


    my_list.delete_link(20)
    print(my_list)


if __name__ == '__main__':
    main()