python - Add tkinter's intvar to an integer

Question

I'm having some trouble adding a value taken from an Entry box and adding it to an existing number. In this case, I want the value of the "change speed" box to be added to the robots current speed. When run, my code produces an error:

TypeError: unsupported operand type(s) for +=: 'int' and 'IntVar'.

Below is the code that produces the entry box:

change_speed_entry = ttk.Entry(main_frame, width=5)  # Entry box for linear speed
change_speed_entry.grid()
data = tkinter.IntVar()
change_speed_entry['textvariable'] = data

And next is where I try to manipulate the result. This is a method within a class. All other methods of the class work correctly:

def changeSpeed(self, delta_speed):
    self.speed += delta_speed

Answer 1

You need to first invoke the .get method of IntVar:

def changeSpeed(self, delta_speed):
    self.speed += delta_speed.get()

which returns the variable's value as an integer.

Since I don't have your full code, I wrote a small script to demonstrate:

from Tkinter import Entry, IntVar, Tk

root = Tk()

data = IntVar()

entry = Entry(textvariable=data)
entry.grid()

def click(event):
    # Get the number, add 1 to it, and then print it
    print data.get() + 1

# Bind the entrybox to the Return key
entry.bind("<Return>", click)

root.mainloop()

When you run the script, a small window appears that has an entrybox. When you type a number in that entrybox and then click Return, the script gets the number stored in data (which will be the number you typed in), adds 1 to it, and then prints it on the screen.