Progressbar with Percentage Label?

This is possible using a ttk.Style. The idea is to modify the layout of the Horizontal.TProgressbar style (do the same with Vertical.TProgressbar for a vertical progressbar) to add a label inside the bar:

Usual Horizontal.TProgressbar layout:

[('Horizontal.Progressbar.trough',
  {'children': [('Horizontal.Progressbar.pbar',
     {'side': 'left', 'sticky': 'ns'})],
   'sticky': 'nswe'})]

With an additional label:

[('Horizontal.Progressbar.trough',
  {'children': [('Horizontal.Progressbar.pbar',
     {'side': 'left', 'sticky': 'ns'})],
   'sticky': 'nswe'}),
 ('Horizontal.Progressbar.label', {'sticky': 'nswe'})]

Then, the text of the label can be changed with style.configure.

Here is the code:

import tkinter as tk
from tkinter import ttk

root = tk.Tk()

style = ttk.Style(root)
# add label in the layout
style.layout('text.Horizontal.TProgressbar', 
             [('Horizontal.Progressbar.trough',
               {'children': [('Horizontal.Progressbar.pbar',
                              {'side': 'left', 'sticky': 'ns'})],
                'sticky': 'nswe'}), 
              ('Horizontal.Progressbar.label', {'sticky': 'nswe'})])
# set initial text
style.configure('text.Horizontal.TProgressbar', text="0 %", anchor="center")
# create progressbar
variable = tk.DoubleVar(root)
pbar = ttk.Progressbar(root, style="text.Horizontal.TProgressbar", variable=variable)
pbar.pack()

def increment():
    pbar.step()  # increment progressbar 
    style.configure('text.Horizontal.TProgressbar', 
                    text="{:g} %".format(variable.get()))  # update label
    root.after(200, increment)
    
increment()

root.mainloop()

Styling

The font, color and position of the label can be changed using style.configure. For instance,

style.configure('text.Horizontal.TProgressbar', foreground="red", 
                font="Arial 20", anchor="w")

gives

Multiple progressbars

The text is set through the style therefore to have multiple progressbars with different labels, one needs to use a different style for each. However, there is no need to set the layout for each style: create the layout 'text.Horizontal.TProgressbar' like in the above code and then use substyles 'pb1.text.Horizontal.TProgressbar', 'pb2.text.Horizontal.TProgressbar', … for each progressbar. Then the text of a single progressbar can be changed with

style.configure('pb1.text.Horizontal.TProgressbar', text=...)