So I basically have written a program in python using tkinter and urllib.request which is supposed to work as a downloader, but each downloader has to have a pause or cancel button but I can’t seem to find anyway to do this! Recently I bumped into the same question in stackoverflow( the link: Is it possible to stop (cancel) urlretrieve process?) and it seems like that I have to use threads or multi-processing but I don’t have a single idea how to do this! By the way how is threading or multi-processing going to help with the canceling pausing the download? Can someone explain to me what should I do? Is there anyway to do this without threading or multi-processing? If there is not, can you explain how to use threading or multi-processing in this program because I don’t have a single clue what to do! Please help me out on this. My code:
from tkinter import *
from tkinter import font as tkFont
import random
import urllib.request
import requests
def printsth():
print("Yay it works! ")
def main_menu():
root = Tk()
root.title('8-bit downloader ')
root.iconbitmap(r"C:UsersrayanraveshPycharmProjectsGUI_Calculatoricon.ico")
root.geometry("600x280")
# the top menu
num = IntVar()
chum = IntVar()
# var = IntVar()
menu = Menu(root)
root.config(menu=menu)
submenu = Menu(menu)
menu.add_cascade(label="Settings", menu=submenu)
def custom_op():
custom = Toplevel()
custom.iconbitmap(r"C:UsersrayanraveshPycharmProjectsGUI_Calculatoricon.ico")
submenu.add_command(label="Customization ", command=custom_op)
def settings_op():
global gps
set_win = Toplevel()
set_win.iconbitmap(r"C:UsersrayanraveshPycharmProjectsGUI_Calculatoricon.ico")
path_label = Label(set_win, text="Current default download path: ")
path_entry = Entry(set_win, width=30)
file_read = open('Data.txt', 'r')
data_base = file_read.read()
path_entry.insert(0, data_base)
file_read.close()
def default_output():
global location
file_read2 = open('Data.txt', 'r+')
file_read2.truncate(0)
file_read2.close()
write_file2 = open('Data.txt', 'w')
write_file2.write(path_entry.get())
write_file2.close()
location = path_entry.get() + "\"
default_location = location.replace("\", "\\")
path_btn = Button(set_win, text="Submit ", command=default_output)
path_label.pack(anchor=CENTER, expand=1)
path_entry.pack(anchor=CENTER, expand=1)
path_btn.pack(anchor=CENTER, expand=1)
submenu.add_command(label="Settings ", command=settings_op)
submenu.add_separator()
submenu.add_command(label="Exit", command=root.destroy)
# the section menu
editmenu = Menu(menu)
menu.add_cascade(label="Sections(soon)", menu=editmenu)
editmenu.add_command(label="Downloader", command=printsth)
editmenu.add_command(label="Converter", command=printsth)
editmenu.add_command(label="Media Player", command=printsth)
editmenu.add_command(label="Editor", command=printsth)
# the tool bar
toolbar = Frame(root, bg="light gray")
insert_button = Button(toolbar, text="Insert an image", command=printsth)
insert_button.pack(side=LEFT, padx=2, pady=2)
print_button = Button(toolbar, text="Print", command=printsth)
print_button.pack(side=LEFT, padx=2, pady=2)
toolbar.pack(side=TOP, fill=X)
# the download function
def download_image():
global formatname
if num.get() == 1:
name = random.randrange(1, 1000000)
else:
name = str(name_entry.get())
formatname = str(format_entry.get())
'''if var.get() == 1:
operator = str(url_entry.get())
formatname = '.' + operator[-3] + operator[-2] + operator[-1]
else:
pass'''
fullname = str(name) + formatname
url = str(url_entry.get())
fw = open('file-size.txt', 'w')
file_size = int(requests.head(url, headers={'accept-encoding': ''}).headers['Content-Length'])
fw.write(str(file_size))
fw.close()
if chum.get() == 1:
filee = open('Data.txt', 'r')
destination = filee.read()
path = destination
output_entry.insert(0, destination)
filee.close()
else:
output_entry.delete(0, END)
path = str(output_entry.get()) + "\"
urllib.request.urlretrieve(url, path.replace("\", "\\") + fullname)
# the status bar
status_bar = Label(root, text="Downloading...", bd=1, relief=SUNKEN, anchor=W)
status_bar.pack(side=BOTTOM, fill=X)
# the download frame
body_frame = Frame(root, bg="light blue")
download_button = Button(body_frame, text="Download! ", command=download_image, border=3, width=20, height=5)
download_design = tkFont.Font(size=12, slant='italic')
download_button['font'] = download_design
download_button.pack(side=LEFT, pady=5, padx=5)
body_frame.pack(side=LEFT, fill=Y)
# the main interaction menu
inter_frame = Frame(root)
url_entry = Entry(inter_frame, width=30)
label = Label(inter_frame, text="Enter the image URL: ")
file_format = Label(inter_frame, text="Choose your file format: ")
format_entry = Entry(inter_frame, width=30)
file_name = Label(inter_frame, text="File's name: ")
name_entry = Entry(inter_frame, width=30)
check_name = Checkbutton(inter_frame, text="Give a random name", variable=num)
# check_format = Checkbutton(inter_frame, text="Download with default format", variable=var)
check_default = Checkbutton(inter_frame, text="Download to default path", variable=chum)
output_path = Label(inter_frame, text="Choose output path: ")
output_entry = Entry(inter_frame, width=30)
file_name.pack(anchor=CENTER, expand=1)
name_entry.pack(anchor=CENTER, expand=1)
check_name.pack(anchor=CENTER, expand=1)
label.pack(anchor=CENTER, expand=1)
url_entry.pack(anchor=CENTER, expand=1)
file_format.pack(anchor=CENTER, expand=1)
format_entry.pack(anchor=CENTER, expand=1)
format_entry.insert(0, '.')
# check_format.pack(anchor=CENTER)
output_path.pack(anchor=CENTER, expand=1)
output_entry.pack(anchor=CENTER, expand=1)
check_default.pack(anchor=CENTER, expand=1)
inter_frame.pack(expand=1)
root.mainloop()
# the end!
main_menu()
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Answer
When running a function like urlretrieve in a single thread or process, there is no way to stop it because there is only one thread or process.
In this case, you are calling urlretrieve from a tkinter callback. Those are called by tkinter from the mainloop, effectively interrupting the mainloop.
This might not be a problem for a small download from a host on a fast connection. But if the download takes second or minutes then you have a problem. Because while urlretrieve is in progress, your GUI is unresponsive because the mainloop is waiting for your callback to finish.
So even if you were to have a “Cancel” button, it would not respond als long as urlretrieve is running.
Read the urlretrieve function from the file urllib/request.py in your Python directory. It’s not a big function and should be relatively easy to follow.
Internally, urlretrieve contains a loop that reads from a URL and writes to a file. By defaults, such reads wait until there is anything to read. The thing is; there is no way to interrupt this loop.
So one way or another, you will have to re-write urlretrieve. In this re-written version you should check in every iteration of the inner loop if you should continue.
You basically have two options;
- Work the functionality of
urlretrieveinto the event loop. - Work the functionality of
urlretrieveinto a different thread.
Each has their pros and cons. If you are using Python 3, starting a threading.Thread is probably the easiest thing to do because tkinter in Python 3 is thread-safe.
For an example of the first approach, see unlock-excel.pyw from my scripts repo on github. In this application, a long operation is divided into several small steps that are called from the tkinter eventloop via the after method.
I don’t have an example handy for the method with using a thread. Basically you have to rewrite urlretrieve to check a variable (e.g. a threading.Event) that signals if it should stop in the inner while loop.