Open printer selection window in Tkinter

Question

I am having a problem possibly due to my lack of knowledge. I want to open the windows dialog to choose printer and send to print (to a printer) using Tkinter.

Currently, I use a code to relate Tkinter to Wxpython and make it asynchronous creating a separate process.

This is the code mentioned above:

from tkinter import *
from threading import Thread
import wx

def f_imprimir(ventana, entry):
    class TextDocPrintout(wx.Printout):
        def __init__(self):
            wx.Printout.__init__(self)

        def OnPrintPage(self, page):
            dc = self.GetDC()

            ppiPrinterX, ppiPrinterY = self.GetPPIPrinter()     
            ppiScreenX, ppiScreenY = self.GetPPIScreen()     
            logScale = float(ppiPrinterX)/float(ppiScreenX)

            pw, ph = self.GetPageSizePixels()
            dw, dh = dc.GetSize()     
            scale = logScale * float(dw)/float(pw)
            dc.SetUserScale(scale, scale)

            logUnitsMM = float(ppiPrinterX)/(logScale*25.4)

            ### Print code ###

            return True

    class PrintFrameworkSample(wx.Frame):        
        def OnPrint(self):
            pdata = wx.PrintData()
            pdata.SetPaperId(wx.PAPER_A4)
            pdata.SetOrientation(wx.LANDSCAPE)

            data = wx.PrintDialogData(pdata)
            printer = wx.Printer(data)

            printout = TextDocPrintout()

            useSetupDialog = True

            if not printer.Print(self, printout, useSetupDialog) and printer.GetLastError() == 
wx.PRINTER_ERROR:

                wx.MessageBox(

                    "There was a problem printing.\n"

                    "Perhaps your current printer is not set correctly?",

                    "Printing Error", wx.OK)

            else:
                data = printer.GetPrintDialogData() 
                pdata = wx.PrintData(data.GetPrintData()) # force a copy

            printout.Destroy()
            self.Destroy()

    app=wx.App(False)
    PrintFrameworkSample().OnPrint()
    entry.config(state="normal")


def process(ventana, entry):
    entry.config(state="disable")
    t = Thread(target=f_imprimir, args=(ventana,entry))
    t.start()

v = Tk()
entry = Entry(v)
entry.pack()
v.bind("a", lambda a:process(v,entry))

when wx.app finishes, which can happen when the Printer Selector closes, I plan to change the status of the entry to "normal". But it throws an error when changing the state of the entry to "normal", which I suppose is because the window and the order I send are in separate processes. The error would be:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "C:\Python38-32\lib\threading.py", line 932, in _bootstrap_inner
    self.run()
  File "C:\Python38-32\lib\threading.py", line 870, in run
    self._target(*self._args, **self._kwargs)
  File "C:\Users\DANTE\Google Drive\JNAAB\DESARROLLO\pruebas\pedasito.py", line 65, in f_imprimir
    entry.config(state="normal")
  File "C:\Python38-32\lib\tkinter\__init__.py", line 1637, in configure
    return self._configure('configure', cnf, kw)
  File "C:\Python38-32\lib\tkinter\__init__.py", line 1627, in _configure
    self.tk.call(_flatten((self._w, cmd)) + self._options(cnf))
RuntimeError: main thread is not in main loop

Does anyone have a solution for this problem or an alternative way to create the print window without blocking the TCL window and being able to block the entry? If there is a way to do it or send to print using Tkinter and avoid this mess it would be even better. Thank you.

Answer 1

I dont use wxPython however your error is due to a threading issue related to tkinter. Tkinter likes to be in the main thread and trying to pass widgets to a seperate thread can cause problems. However your entry field is in the global namespace already so you do not need to pass it.

Simply updated from your thread once it needs to be.

I would do this in your if/else condition so it only happens at the correct time.

Something like this would work: Note you will need to actually do something with the value passed. As it is now none of your code actually prints anything other than a blank page.

import tkinter as tk
from threading import Thread
import wx


def f_imprimir(value):
    # here you can see the value of entry was passed as a string so we can avoid any issues with the widget
    print(value)
    class TextDocPrintout(wx.Printout):
        def __init__(self):
            wx.Printout.__init__(self)

        def OnPrintPage(self, page):
            dc = self.GetDC()
            ppiPrinterX, ppiPrinterY = self.GetPPIPrinter()     
            ppiScreenX, ppiScreenY = self.GetPPIScreen()     
            logScale = float(ppiPrinterX)/float(ppiScreenX)

            pw, ph = self.GetPageSizePixels()
            dw, dh = dc.GetSize()     
            scale = logScale * float(dw)/float(pw)
            dc.SetUserScale(scale, scale)
            logUnitsMM = float(ppiPrinterX)/(logScale*25.4)
            return True

    class PrintFrameworkSample(wx.Frame):        
        def OnPrint(self):
            pdata = wx.PrintData()
            pdata.SetPaperId(wx.PAPER_A4)
            pdata.SetOrientation(wx.LANDSCAPE)
            data = wx.PrintDialogData(pdata)
            printer = wx.Printer(data)
            printout = TextDocPrintout()
            useSetupDialog = True

            if not printer.Print(self, printout, useSetupDialog) and printer.GetLastError() == wx.PRINTER_ERROR:

                wx.MessageBox("There was a problem printing.\n\n"
                              "Perhaps your current printer is not set correctly?\n\n"
                              "Printing Error", wx.OK)
                entry.config(state="normal")
            else:
                data = printer.GetPrintDialogData() 
                pdata = wx.PrintData(data.GetPrintData())  # force a copy
                entry.config(state="normal")

            printout.Destroy()
            self.Destroy()

    app = wx.App(False)
    PrintFrameworkSample().OnPrint()



def process(_=None):
    entry.config(state="disable")
    t = Thread(target=f_imprimir, args=(entry.get(),))
    t.start()


v = tk.Tk()
entry = tk.Entry(v)
entry.pack()
v.bind("<Return>", process)
v.mainloop()