How to change the color of certain words in the tkinter text widget?

The main idea is to apply tags to the parts of text you want to customise. You can create your tags using the method tag_configure, with a specific style, and then you just need to apply this tag to the part of text you want to change using the method tag_add.
You can also remove the tags using the method tag_remove.

The following is an example that uses tag_configure, tag_add and tag_remove methods.

#!/usr/bin/env python3

import tkinter as tk
from tkinter.font import Font

class Pad(tk.Frame):

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

        self.toolbar = tk.Frame(self, bg="#eee")
        self.toolbar.pack(side="top", fill="x")

        self.bold_btn = tk.Button(self.toolbar, text="Bold", command=self.make_bold)

        self.clear_btn = tk.Button(self.toolbar, text="Clear", command=self.clear)

        # Creates a bold font
        self.bold_font = Font(family="Helvetica", size=14, weight="bold")

        self.text = tk.Text(self)
        self.text.insert("end", "Select part of text and then click 'Bold'...")
        self.text.pack(fill="both", expand=True)

        # configuring a tag called BOLD
        self.text.tag_configure("BOLD", font=self.bold_font)

    def make_bold(self):
        # tk.TclError exception is raised if not text is selected
            self.text.tag_add("BOLD", "sel.first", "sel.last")        
        except tk.TclError:

    def clear(self):
        self.text.tag_remove("BOLD",  "1.0", 'end')

def demo():
    root = tk.Tk()
    Pad(root).pack(expand=1, fill="both")

if __name__ == "__main__":

If you don’t know what sel.first and sel.last are, check out this post or this reference.

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