NameError while using Global Variables-CodePudding

I am working on a project in Python with Pycharm as my code-editor. In my code I faced variable not defined error in spite of declaring it as Global. Here's the code snippet:

global hpw
global mil


def bt_cars(hpw, mil):
  hpw = StringVar()
  mil = StringVar()
  w1 = Toplevel()
  w1.title("Choose Features")
  w1.geometry("430x200")

  lb3 = Label(w1, text="Choose features for comparison", bg="yellow"
            , font=('Arial Black', 18), width=25)
  lb4 = Label(w1, text=" ", anchor=tk.CENTER)
  fr1 = LabelFrame(w1, width=20, padx=100)
  hp_cb = Checkbutton(fr1, text="Horsepower", variable=hp, anchor='w', onvalue="Horsepower", offvalue=" ")
  hpw_cb.grid()
  hpw_cb.deselect()
  mil_cb = Checkbutton(fr1, text="Mileage", variable=mi, anchor='w', onvalue="Mileage", offvalue=" ")
  mil_cb.grid()
  mil_cb.deselect()

  lb3.grid(row=0, column=1)
  lb4.grid(row=1, column=1)
  fr1.grid(row=2, column=1)
  root.withdraw()


bt1 = Button(root, text="CARS", width=5, font=('Calibri', 15), command=bt_cars)
bt1.grid(row=7)

space2 = Label(root, text="\n\n")
space2.grid(row=6)

var_stor1 = [mil, hpw]   #NameError here, python doesn't recognise mil and hpw

for i in var_stor1:
   if i.get() != " ":
     work_stor.append(i)
print(work_stor)

root.mainloop()

The error for this code:

C:\Users\bspoo\AppData\Local\Programs\Python\Python310-32\python.exe "E:/Software/Python    /Programs/School/Project SPASC/SPASC II.py"
Traceback (most recent call last):
File "E:\Software\Python\Programs\School\Project SPASC\SPASC II.py", line 55, in <module>
var_stor1 = [mil, hpw]
NameError: name 'mil' is not defined. Did you mean: 'min'?

What should I do to overcome this error?

*NOTE: This is only part of my code. So please ignore if import tkinter is missing

CodePudding user response：

The simple answer is to get rid of the global statements in the global scope and put them in bt_cars instead:

# Get rid of these altogether
# global hpw
# global mil


def bt_cars():  # Button callbacks are not called with any arguments
    global hpw, mil

    # Are these the assignments you want?
    hpw = StringVar()
    mil = StringVar()
    ...

If you want to use hpw and mil in the global scope, you need to either define them before bt_cars is called, or you need to ensure that bt_cars is called before you try to use hpw or mil.

CodePudding user response：

In order to change the value of a global variable inside a function, you must declare it global inside the function.

You should check the file of ASCII .line 55

CodePudding user response：

You need to go back to fundamentals of functions and function parameters and the scope of variables in python. Please go through all the comments I have added in your code. Also, There is very little clarity about what you are trying to do here. I hope it will clarify things for you:

from tkinter import *

root = Tk()
# global hpw
# global mil
# Please initialize the variables with an argument for the function or directly use a value as an argument in yout function
# for example, no need of global keyword, following variables already have a global scope:
hpw = 'a'
mil = 'b'
# it isnt necessary for these variables to be named same as function parameter. The function parameters have a scope local to the function.


def bt_cars(hpw, mil):
    # hpw and mil have a scope local to the function. Also I dont understand their use as in your function you havent used hpw and mil anywhere.
    hp = StringVar()  # Do you mean this hp is the hpw you intended
    mi = StringVar()  # Do you mean this mi is the mil you intended
    w1 = Toplevel()
    w1.title("Choose Features")
    w1.geometry("430x200")

    lb3 = Label(w1, text="Choose features for comparison",
                bg="yellow", font=('Arial Black', 18), width=25)
    lb4 = Label(w1, text=" ", anchor=CENTER)
    fr1 = LabelFrame(w1, width=20, padx=100)
    hp_cb = Checkbutton(fr1, text="Horsepower", variable=hp,
                        anchor='w', onvalue="Horsepower", offvalue=" ")
    hp_cb.grid()
    hp_cb.deselect()
    mil_cb = Checkbutton(fr1, text="Mileage", variable=mi,
                         anchor='w', onvalue="Mileage", offvalue=" ")
    mil_cb.grid()
    mil_cb.deselect()

    lb3.grid(row=0, column=1)
    lb4.grid(row=1, column=1)
    fr1.grid(row=2, column=1)
    root.withdraw()


# The function arguments here?? You could use lambda here
bt1 = Button(root, text="CARS", width=5, font=('Calibri', 15), command=bt_cars)
bt1.grid(row=7)

space2 = Label(root, text="\n\n")
space2.grid(row=6)

var_stor1 = [hpw, mil]  # There wont be any error now.