How to Implement a Progress Bar in Python

To implement a progress bar in Python, write a function that takes its arguments the progress in percentages, and the width of the bar. Then, based on the percentage:

Calculate the number of hashtags on the left.
Calculate the number of spaces on the right.
Print the hashtags, spaces, and percentages on the same line.

If you only came for the code, here it is with an example use:

from time import sleep

def progress(percent=0, width=40):
    left = width * percent // 100
    right = width - left
    
    tags = "#" * left
    spaces = " " * right
    percents = f"{percent:.0f}%"
    
    print("\r[", tags, spaces, "]", percents, sep="", end="", flush=True)

# Example run
for i in range(101):
    progress(i)
    sleep(0.05)

This outputs a progress bar that fills up among the percentage.

[#################################             ] 75%

Next, let’s go through the code in detail to understand what happens.

Implementation of Progress Bar in Python

Let’s start with the 4th and 5th lines:

left = width * percent // 100
right = width - left

Here the left is the number of hashtags given the progress percentage. For example, at 30% it is (40 * 30) / 100 = 12. The right is the number of spaces on the right-hand side. In the case of 30% progress, it is 40 – 12 = 28.

On lines 7 and 8, we multiply a hashtag/empty space by the number of times they should occur:

tags = "#" * left
spaces = " " * right

On line 10, we format the number of percents to be displayed in the mix:

percents = f"{percent:.0f}%"

On line 12, we put it all together and print the hashtags, spaces, and percentages. There is so much going on in this line.

print("\r[", tags, spaces, "]", percents, sep="", end="", flush=True)

Let’s take a deeper look at each part of the line:

“\r[“ always prints “[“ on the same place in the line. The \r is called a carriage return. It always goes back to the same starting point of the line.
Then we add the tags, spaces, closing square bracket, and the percentage. This is all we need for the progress bar itself.
Next, we specify an optional parameter sep. It acts as the separator between each printed item. By default, it is a space. But we do not want space so we specify it as an empty string “”.
Then we tweak the end argument. By default, Python print() adds a line break at the end of the line. But this is not what we want. So we also specify the end as an empty string.
Finally, the flush is set to True. By default, Python does not display consecutive print() calls if they do not have line breaks. This is due to buffering, which optimizes performance.