Global variable doesn't accept change in python

Question

I created a small program to select a file and then display the filepath using print OUTSIDE the openfile function (I need to access the file_path variable outside because I plan on using it for other stuff). I declared it as a global variable but the output is still empty. When I use print(file_path) inside the openfile function it works perfectly. I’m new to programming so bear with. TYIW

from tkinter import *
from tkinter import filedialog as fd
import pyperclip

file_path = ''

def OpenFile():
    global file_path
    file_path = fd.askopenfilename()


print(file_path)
#GUI
window = Tk()
window.geometry('600x600')



Open_button = Button(window,text='Select File', command=OpenFile)
Open_button.pack()

window.mainloop()

Asked By: refrain

||

Source

Answer 1

You are calling the function after you print the value, so it has not yet changed when you print.

Try to print the value after the function is called.

Answered By: Chris

Answer 2

Python is an interpreter based language, So it read’s the code line by line.

file_path = '' # First reads this
 
def OpenFile(): # then reads this function
    global file_path
    file_path = fd.askopenfilename()


print(file_path) # then this

The functions wont execute until you call it. You may have noticed that before printing file_path you havnt called OpenFile function, so the variable file_paths value is ”.

I would to set focus on window.mainloop() function. mainloop is an important part of tkinter application as it tells Python to run Tkinter’s Event loop. This method listens for events, such as button clicks or keypresses, and blocks any code that comes after it from running until you close the window where you called the method.

For more details of mainloop see this answer.

The mainloop checks if any event is been passed, if passed then only updates the tkinter window. mainloop is actually a loop of update() and update_idletask() so it would only execute print(file_path) once unless and untill you have called it multiple times or in another loop.

So there are 3 solution for your problem:

Adding another button and printing through it.

def printing():
    print(file_path)

print_button = Button(window,text='Click to print value:', command=printing)
print_button.pack()

Using text variables:

from tkinter import *
from tkinter import filedialog as fd
import pyperclip

file_path = StringVar()

def OpenFile():
    global file_path
    file_path.set(fd.askopenfilename()) ###

window = Tk()
window.geometry('600x600')



Open_button = Button(window,text='Select File', command=OpenFile)
Open_button.pack()
a=Label(window,textvariable=file_path)
a.pack()

window.mainloop()

Using .config:

def OpenFile():
    global file_path
    file_path = fd.askopenfilename()
    a.config(text=file_path)

Answered By: Faraaz Kurawle

Global variable doesn't accept change in python

Question:

Answers: