Python NotePad Using GUI

from  tkinter import *
import tkinter.messagebox as tmsg
import os,sys
from tkinter.filedialog import askopenfilename,asksaveasfilename,asksaveasfile

root = Tk()
def New():
    global file
    root.title("Untitle - Notepad")
    file = None
    text.delete(1.0,END)
def openfile():
    global file
    file = askopenfilename(defaultextension = ".txt",filetypes=[("All files","*.*"),("Text Documents","*.txt")])
    if file == "":
        file = None
    else:
        root.title(os.path.basename(file) + " - Notepad")
        text.delete(1.0,END)
        f = open(file,"r")
        text.insert(1.0,f.read())
        f.close()

def Save():
    global file
    if file== None:
        file= asksaveasfilename(initialfile='Untitled.txt',filetypes=[("All files","*.*"),("Text Documents",".txt")])
        if file == "":
            file = None
        else:
            f = open(file,"w")
            f.write(text.get(1.0,END))
            f.close()
            root.title(os.path.basename(file) + " - Notepad")
    else:
        f = open(file, "r")
        f.write(text.get(1.0, END))
        f.close()
def Saveas():
    global file
    files=[("All Files","*.*"),
           ("Python Files","*.py"),
           ("Text Document","*.txt")]
    file = asksaveasfile(filetypes = files, defaultextension = files)


def exit():
    root.destroy()
def about():
    tmsg.showinfo("help", "How can help you")

def cut():
    text.event_generate(("<<Cut>>"))
def copy():
    text.event_generate(("<<Copy>>"))
def past():
    text.event_generate(("<<Paste>>"))
if __name__ == '__main__':

    root.title("Untitle - Notepad")

    root.geometry("400x400")
    scrollbar=Scrollbar()
    scrollbar.pack(side=RIGHT,fill=Y)
    var = StringVar()
    text=Text(root,yscrollcommand=scrollbar.set,font="lucida 12 bold")
    file = None
    text.pack(expand=True,fill=BOTH)
    scrollbar.config(command=text.yview)
    mainmenu=Menu(root)
    m1=Menu(mainmenu,tearoff=0)
    m1.add_command(label="New",command=New)
    m1.add_command(label="Open",command=openfile)
    m1.add_command(label="Save",command=Save)
    m1.add_command(label="Save As",command=Saveas)
    m1.add_command(label="Exit",command=exit)

    root.config(menu=mainmenu)
    mainmenu.add_cascade(label="File",menu=m1)
    # copy cut
    m2=Menu(mainmenu,tearoff=0)
    m2.add_command(label="Cut",command=cut)
    m2.add_command(label="Copy",command=copy)
    m2.add_command(label="Past",command=past)
    root.config(menu=mainmenu)
    mainmenu.add_cascade(label="Edit",menu=m2)
    #for help in this menu
    m3=Menu(mainmenu,tearoff=0)
    m3.add_command(label="About As",command=about)

    root.config(menu=mainmenu)
    mainmenu.add_cascade(label="Help",menu=m3)
    root.mainloop()