Tkinter Entry widget sees empty string, cannot convert to float because of it-CodePudding

I'm trying to make a Density/Volume/Mass calculator. When I enter the values in the Entry widgets and click the button, I get a ValueError: could not convert string to float: '' message. What am I missing? Why doesnt it see the entered values? Oddly, I first made only the density calculator part, and it worked perfectly. Now it doesn't.

import tkinter as tk
from tkinter import ttk


def density_calculator():

    def density():
        vol = float(vol_value.get())
        mas = float(mass_value.get())
        dens = mas / vol
        calculated_density = ttk.Label(root, text=f"{dens}", font=("Helvetica", 20))
        calculated_density.place(x=280, y=290)

    density_w = tk.Tk()
    density_w.title("Density Calculator")
    density_w.geometry("600x400")
    density_w.resizable(False, False)
    vol_value = tk.StringVar()
    mass_value = tk.StringVar()
    volume = ttk.Label(density_w, text="Volume (cm^3)", relief="ridge", font=("Helvetica", 20))
    mass = ttk.Label(density_w, text="Mass (g)", relief="ridge", font=("Helvetica", 20))
    density_label = ttk.Label(density_w, text="Density (g/cm3)", relief="ridge", font=("Helvetica", 20))
    volume_entry = ttk.Entry(density_w, textvariable=vol_value)
    mass_entry = ttk.Entry(density_w, textvariable=mass_value)


    volume.place(x=65, y=50)
    mass.place(x=405, y=50)
    density_label.place(x=200, y=250)
    volume_entry.place(x=100, y=100)
    mass_entry.place(x=400, y=100)

    done_button = ttk.Button(density_w, text="Calculate", command=density)
    done_button.place(x=480, y=350)
    density_w.mainloop()


def volume_calculator():


    def volume():
        vol = float(dens_value.get())
        mas = float(mass_value.get())
        dens = mas / vol
        calculated_density = ttk.Label(root, text=f"{dens}", font=("Helvetica", 20))
        calculated_density.place(x=280, y=290)

    volume_w = tk.Tk()
    volume_w.title("Volume Calculator")
    volume_w.geometry("600x400")
    volume_w.resizable(False, False)
    dens_value = tk.StringVar()
    mass_value = tk.StringVar()
    density = ttk.Label(volume_w, text="Density (g/cm^3)", relief="ridge", font=("Helvetica", 20))
    mass = ttk.Label(volume_w, text="Mass (g)", relief="ridge", font=("Helvetica", 20))
    volume_label = ttk.Label(volume_w, text="Volume (cm3)", relief="ridge", font=("Helvetica", 20))
    density_entry = ttk.Entry(volume_w, textvariable=dens_value)
    mass_entry = ttk.Entry(volume_w, textvariable=mass_value)

    density.place(x=65, y=50)
    mass.place(x=405, y=50)
    volume_label.place(x=200, y=250)
    density_entry.place(x=100, y=100)
    mass_entry.place(x=400, y=100)

    done_button = ttk.Button(volume_w, text="Calculate", command=volume)
    done_button.place(x=480, y=350)
    volume_w.mainloop()


root = tk.Tk()
root.title("Density, Volume, Mass Calculator")
root.geometry("200x100")
root.resizable(False, False)


density_choice = ttk.Radiobutton(root, text="Calculate Density", command=density_calculator)
volume_choice = ttk.Radiobutton(root, text="Calculate Volume", command=volume_calculator)
mass_choice = ttk.Radiobutton(root, text="Calculate Density")
density_choice.place(x=0, y=0)
volume_choice.place(x=0, y=20)

root.mainloop()

CodePudding user response：

After changing the following two things your code is now working fine

Replace StringVar variable with entry variable when getting value
Use actual window name in the Label creation for showing result

Final code is following

import tkinter as tk
from tkinter import ttk


def density_calculator():

    def density():
        vol = float(volume_entry.get())
        mas = float(mass_entry.get())
        dens = round(mas / vol, 2)
        calculated_density = ttk.Label(density_w, text=f"{dens}", font=("Helvetica", 20))
        calculated_density.place(x=280, y=290)

    density_w = tk.Tk()
    density_w.title("Density Calculator")
    density_w.geometry("600x400")
    density_w.resizable(False, False)
    vol_value = tk.StringVar()
    mass_value = tk.StringVar()
    volume = ttk.Label(density_w, text="Volume (cm^3)", relief="ridge", font=("Helvetica", 20))
    mass = ttk.Label(density_w, text="Mass (g)", relief="ridge", font=("Helvetica", 20))
    density_label = ttk.Label(density_w, text="Density (g/cm3)", relief="ridge", font=("Helvetica", 20))
    volume_entry = ttk.Entry(density_w, textvariable=vol_value)
    mass_entry = ttk.Entry(density_w, textvariable=mass_value)


    volume.place(x=65, y=50)
    mass.place(x=405, y=50)
    density_label.place(x=200, y=250)
    volume_entry.place(x=100, y=100)
    mass_entry.place(x=400, y=100)

    done_button = ttk.Button(density_w, text="Calculate", command=density)
    done_button.place(x=480, y=350)
    density_w.mainloop()


def volume_calculator():


    def volume():
        vol = float(density_entry.get())
        mas = float(mass_entry.get())
        dens = round(mas / vol, 2)
        calculated_density = ttk.Label(volume_w, text=f"{dens}", font=("Helvetica", 20))
        calculated_density.place(x=280, y=290)

    volume_w = tk.Tk()
    volume_w.title("Volume Calculator")
    volume_w.geometry("600x400")
    volume_w.resizable(False, False)
    dens_value = tk.StringVar()
    mass_value = tk.StringVar()
    density = ttk.Label(volume_w, text="Density (g/cm^3)", relief="ridge", font=("Helvetica", 20))
    mass = ttk.Label(volume_w, text="Mass (g)", relief="ridge", font=("Helvetica", 20))
    volume_label = ttk.Label(volume_w, text="Volume (cm3)", relief="ridge", font=("Helvetica", 20))
    density_entry = ttk.Entry(volume_w, textvariable=dens_value)
    mass_entry = ttk.Entry(volume_w, textvariable=mass_value)

    density.place(x=65, y=50)
    mass.place(x=405, y=50)
    volume_label.place(x=200, y=250)
    density_entry.place(x=100, y=100)
    mass_entry.place(x=400, y=100)

    done_button = ttk.Button(volume_w, text="Calculate", command=volume)
    done_button.place(x=480, y=350)
    volume_w.mainloop()


root = tk.Tk()
root.title("Density, Volume, Mass Calculator")
root.geometry("200x100")
root.resizable(False, False)


density_choice = ttk.Radiobutton(root, text="Calculate Density", command=density_calculator)
volume_choice = ttk.Radiobutton(root, text="Calculate Volume", command=volume_calculator)
mass_choice = ttk.Radiobutton(root, text="Calculate Density")
density_choice.place(x=0, y=0)
volume_choice.place(x=0, y=20)

root.mainloop()

Output is Following