Python Logging to Tkinter Text Widget

Question

In addition to the above answers: even though there are a lot of proposed solutions for this (here and also in this other thread), I was struggling quite a bit to make this work myself. Eventually I ran into this text handler class by Moshe Kaplan, which uses a ScrolledText widget (which is probably easier than the ScrollBar method).

It took me some time to figure out how to actually use Moshe's class in a threaded application. In the end I created a minimal demo script that shows how to make it all work. As it might be helpful to others I'm sharing it below. In my particular case I wanted to log to both the GUI and to a text file; if you don't need that just remove the filename attribute in logging.basicConfig.

import time
import threading
import logging
try:
    import tkinter as tk # Python 3.x
    import tkinter.scrolledtext as ScrolledText
except ImportError:
    import Tkinter as tk # Python 2.x
    import ScrolledText

class TextHandler(logging.Handler):
    # This class allows you to log to a Tkinter Text or ScrolledText widget
    # Adapted from Moshe Kaplan: https://gist.github.com/moshekaplan/c425f861de7bbf28ef06

    def __init__(self, text):
        # run the regular Handler __init__
        logging.Handler.__init__(self)
        # Store a reference to the Text it will log to
        self.text = text

    def emit(self, record):
        msg = self.format(record)
        def append():
            self.text.configure(state='normal')
            self.text.insert(tk.END, msg + '\n')
            self.text.configure(state='disabled')
            # Autoscroll to the bottom
            self.text.yview(tk.END)
        # This is necessary because we can't modify the Text from other threads
        self.text.after(0, append)

class myGUI(tk.Frame):

    # This class defines the graphical user interface 

    def __init__(self, parent, *args, **kwargs):
        tk.Frame.__init__(self, parent, *args, **kwargs)
        self.root = parent
        self.build_gui()

    def build_gui(self):                    
        # Build GUI
        self.root.title('TEST')
        self.root.option_add('*tearOff', 'FALSE')
        self.grid(column=0, row=0, sticky='ew')
        self.grid_columnconfigure(0, weight=1, uniform='a')
        self.grid_columnconfigure(1, weight=1, uniform='a')
        self.grid_columnconfigure(2, weight=1, uniform='a')
        self.grid_columnconfigure(3, weight=1, uniform='a')

        # Add text widget to display logging info
        st = ScrolledText.ScrolledText(self, state='disabled')
        st.configure(font='TkFixedFont')
        st.grid(column=0, row=1, sticky='w', columnspan=4)

        # Create textLogger
        text_handler = TextHandler(st)

        # Logging configuration
        logging.basicConfig(filename='test.log',
            level=logging.INFO, 
            format='%(asctime)s - %(levelname)s - %(message)s')        

        # Add the handler to logger
        logger = logging.getLogger()        
        logger.addHandler(text_handler)

def worker():
    # Skeleton worker function, runs in separate thread (see below)   
    while True:
        # Report time / date at 2-second intervals
        time.sleep(2)
        timeStr = time.asctime()
        msg = 'Current time: ' + timeStr
        logging.info(msg) 

def main():

    root = tk.Tk()
    myGUI(root)

    t1 = threading.Thread(target=worker, args=[])
    t1.start()

    root.mainloop()
    t1.join()

main()

Github Gist link to above code here:

https://gist.github.com/bitsgalore/901d0abe4b874b483df3ddc4168754aa

You should subclass logging.Handler, e.g.:

import logging
from Tkinter import INSERT

class WidgetLogger(logging.Handler):
    def __init__(self, widget):
        logging.Handler.__init__(self)
        self.widget = widget

    def emit(self, record):
        # Append message (record) to the widget
        self.widget.insert(INSERT, record + '\n')

I built on Yuri's idea, but needed to make a few changes to get things working:

import logging
import Tkinter as tk

class WidgetLogger(logging.Handler):
    def __init__(self, widget):
        logging.Handler.__init__(self)
        self.setLevel(logging.INFO)
        self.widget = widget
        self.widget.config(state='disabled')

    def emit(self, record):
        self.widget.config(state='normal')
        # Append message (record) to the widget
        self.widget.insert(tk.END, self.format(record) + '\n')
        self.widget.see(tk.END)  # Scroll to the bottom
        self.widget.config(state='disabled')

Note that toggling the state back and forth from 'normal' to 'disabled' is necessary to make the Text widget read-only.

Building further on ford's answer, here's a scrolling Text widget that tails the log. The logging_handler member is what you add to your logger.

import logging
from Tkinter import END, N, S, E, W, Scrollbar, Text
import ttk

class LoggingHandlerFrame(ttk.Frame):

    class Handler(logging.Handler):
        def __init__(self, widget):
            logging.Handler.__init__(self)
            self.setFormatter(logging.Formatter("%(asctime)s: %(message)s"))
            self.widget = widget
            self.widget.config(state='disabled')

        def emit(self, record):
            self.widget.config(state='normal')
            self.widget.insert(END, self.format(record) + "\n")
            self.widget.see(END)
            self.widget.config(state='disabled')

    def __init__(self, *args, **kwargs):
        ttk.Frame.__init__(self, *args, **kwargs)

        self.columnconfigure(0, weight=1)
        self.columnconfigure(1, weight=0)
        self.rowconfigure(0, weight=1)

        self.scrollbar = Scrollbar(self)
        self.scrollbar.grid(row=0, column=1, sticky=(N,S,E))

        self.text = Text(self, yscrollcommand=self.scrollbar.set)
        self.text.grid(row=0, column=0, sticky=(N,S,E,W))

        self.scrollbar.config(command=self.text.yview)

        self.logging_handler = LoggingHandlerFrame.Handler(self.text)

Building on ford's too but adding colored text !

class WidgetLogger(logging.Handler):
    def __init__(self, widget):
        logging.Handler.__init__(self)
        self.setLevel(logging.DEBUG)
        self.widget = widget
        self.widget.config(state='disabled')
        self.widget.tag_config("INFO", foreground="black")
        self.widget.tag_config("DEBUG", foreground="grey")
        self.widget.tag_config("WARNING", foreground="orange")
        self.widget.tag_config("ERROR", foreground="red")
        self.widget.tag_config("CRITICAL", foreground="red", underline=1)

        self.red = self.widget.tag_configure("red", foreground="red")
    def emit(self, record):
        self.widget.config(state='normal')
        # Append message (record) to the widget
        self.widget.insert(tk.END, self.format(record) + '\n', record.levelname)
        self.widget.see(tk.END)  # Scroll to the bottom
        self.widget.config(state='disabled') 
        self.widget.update() # Refresh the widget