Simple GUI calculator using Tkinter

from tkinter import *

expression = ""

def press(num):

global expression

expression = expression + str(num)

equation.set(expression)

def equalpress():

try:

global expression

total = str(eval(expression))

equation.set(total)

expression = ""

except:

equation.set(" error ")

expression = ""

def clear():

global expression

expression = ""

equation.set("")

if __name__ == "__main__":

gui = Tk()

gui.configure(background="light green")

gui.title("Simple Calculator")

gui.geometry("270x150")

equation = StringVar()

expression_field = Entry(gui, textvariable=equation)

expression_field.grid(columnspan=4, ipadx=70)

button1 = Button(gui, text=' 1 ', fg='black', bg='red',

command=lambda: press(1), height=1, width=7)

button1.grid(row=2, column=0)

button2 = Button(gui, text=' 2 ', fg='black', bg='red',

command=lambda: press(2), height=1, width=7)

button2.grid(row=2, column=1)

button3 = Button(gui, text=' 3 ', fg='black', bg='red',

command=lambda: press(3), height=1, width=7)

button3.grid(row=2, column=2)

button4 = Button(gui, text=' 4 ', fg='black', bg='red',

command=lambda: press(4), height=1, width=7)

button4.grid(row=3, column=0)

button5 = Button(gui, text=' 5 ', fg='black', bg='red',

command=lambda: press(5), height=1, width=7)

button5.grid(row=3, column=1)

button6 = Button(gui, text=' 6 ', fg='black', bg='red',

command=lambda: press(6), height=1, width=7)

button6.grid(row=3, column=2)

button7 = Button(gui, text=' 7 ', fg='black', bg='red',

command=lambda: press(7), height=1, width=7)

button7.grid(row=4, column=0)

button8 = Button(gui, text=' 8 ', fg='black', bg='red',

command=lambda: press(8), height=1, width=7)

button8.grid(row=4, column=1)

button9 = Button(gui, text=' 9 ', fg='black', bg='red',

command=lambda: press(9), height=1, width=7)

button9.grid(row=4, column=2)

button0 = Button(gui, text=' 0 ', fg='black', bg='red',

command=lambda: press(0), height=1, width=7)

button0.grid(row=5, column=0)

plus = Button(gui, text=' + ', fg='black', bg='red',

command=lambda: press("+"), height=1, width=7)

plus.grid(row=2, column=3)

minus = Button(gui, text=' - ', fg='black', bg='red',

command=lambda: press("-"), height=1, width=7)

minus.grid(row=3, column=3)

multiply = Button(gui, text=' * ', fg='black', bg='red',

command=lambda: press("*"), height=1, width=7)

multiply.grid(row=4, column=3)

divide = Button(gui, text=' / ', fg='black', bg='red',

command=lambda: press("/"), height=1, width=7)

divide.grid(row=5, column=3)

equal = Button(gui, text=' = ', fg='black', bg='red',

command=equalpress, height=1, width=7)

equal.grid(row=5, column=2)

clear = Button(gui, text='Clear', fg='black', bg='red',

command=clear, height=1, width=7)

clear.grid(row=5, column='1')

Decimal= Button(gui, text='.', fg='black', bg='red',

command=lambda: press('.'), height=1, width=7)

Decimal.grid(row=6, column=0)

gui.mainloop()

program to rotate doubly linked list by N nodes

class Node:    

    def __init__(self,data):    

        self.data = data;    

        self.previous = None;    

        self.next = None;    

class RotateList:    

    def __init__(self):    

        self.head = None;    

        self.tail = None;    

        self.size = 0;    

    def addNode(self, data):    

        newNode = Node(data);    

        if(self.head == None):    

            self.head = self.tail = newNode;    

            self.head.previous = None;    

            self.tail.next = None;    

        else:    

            self.tail.next = newNode;    

            newNode.previous = self.tail;    

            self.tail = newNode;    

            self.tail.next = None;    

        self.size = self.size + 1;    

    def rotateList(self, n):    

        current = self.head;    

        if(n == 0 or n >= self.size):    

            return;    

        else:   

            for i in range(1, n):    

                current = current.next;                  

            self.tail.next = self.head;    

            self.head = current.next;    

            self.head.previous = None;    

            self.tail = current;    

            self.tail.next = None;              

    def display(self):    

        current = self.head;    

        if(self.head == None):    

            print("List is empty");    

            return;                  

        while(current != None):    

            print(current.data),    

            current = current.next;    

        print();    

dList = RotateList();    

dList.addNode(1);    

dList.addNode(2);    

dList.addNode(3);    

dList.addNode(4);    

dList.addNode(5);    

print("Original List: ");    

dList.display();    

dList.rotateList(3);    

print("Updated List: ");    

dList.display();