Python 3.4 tkinter real-time temperature converter

Question

I wrote complicated program in Python 3.4 (with tkinter gui). It's temperature converter (Celsius to Fahrenheit and reverse) in real-time. It works almost good, but there is one problem. I have to add a space after input value every time. Anyone have idea what's wrong in this program?

from tkinter import *

def cel_na_fahr(event):
    e = ".0"
    a = float(ent1.get())
    a = round((32+9/5*a),2)
    a = str(a)
    if a.endswith(e):
        a=a.replace(".0","")
        ent2.delete(0,END)
        ent2.insert(0,a+event.char)
    else:
        ent2.delete(0,END)
        ent2.insert(0,a+event.char)

def fahr_na_cel(event):
    e = ".0"
    a = float(ent2.get())
    a = round(5/9*(a-32),2)
    a = str(a)
    if a.endswith(e):
        a=a.replace(".0","")
        ent1.delete(0,END)
        ent1.insert(0,a+event.char)
    else:
        ent1.delete(0,END)
        ent1.insert(0,a+event.char)

root = Tk()

root.geometry("300x180+400+400")

fr1 = Frame(root, padx=5, pady=40)
fr1.pack(side=TOP)

fr2 = Frame(root)
fr2.pack(side=TOP)

lbl1 = Label(fr1, text="cel to fahr   ")
lbl1.pack(side=LEFT)

ent1 = Entry(fr1) 
ent1.pack(side=RIGHT)

lbl2 = Label(fr2, text="fahr to cel   ")
lbl2.pack(side=LEFT)

ent2 = Entry(fr2) 
ent2.pack(side=RIGHT)

ent1.bind('<Key>', cel_na_fahr)
ent2.bind('<Key>', fahr_na_cel) 

root.mainloop()

Answer 1

You have to type a space because when the <Key> callback triggers, the key that the user most recently pressed hasn't yet been added to the entry. This is probably what you're trying to compensate for by adding event.char , although you're doing it in the wrong place anyway.

Change your bindings to KeyRelease , so that the callbacks trigger after the entry is updated, and remove the +event.char stuff, as you don't need it any more.

from tkinter import *

def cel_na_fahr(event):
    print(ent1.get())
    e = ".0"
    a = float(ent1.get())
    a = round((32+9/5*a),2)
    a = str(a)
    if a.endswith(e):
        a=a.replace(".0","")
        ent2.delete(0,END)
        ent2.insert(0,a)
    else:
        ent2.delete(0,END)
        ent2.insert(0,a)

def fahr_na_cel(event):
    print(ent2.get())
    e = ".0"
    a = float(ent2.get())
    a = round(5/9*(a-32),2)
    a = str(a)
    if a.endswith(e):
        a=a.replace(".0","")
        ent1.delete(0,END)
        ent1.insert(0,a)
    else:
        ent1.delete(0,END)
        ent1.insert(0,a)

root = Tk()

root.geometry("300x180+400+400")

fr1 = Frame(root, padx=5, pady=40)
fr1.pack(side=TOP)

fr2 = Frame(root)
fr2.pack(side=TOP)

lbl1 = Label(fr1, text="cel to fahr   ")
lbl1.pack(side=LEFT)

ent1 = Entry(fr1) 
ent1.pack(side=RIGHT)

lbl2 = Label(fr2, text="fahr to cel   ")
lbl2.pack(side=LEFT)

ent2 = Entry(fr2) 
ent2.pack(side=RIGHT)

ent1.bind('<KeyRelease>', cel_na_fahr)
ent2.bind('<KeyRelease>', fahr_na_cel) 

root.mainloop()