Not understanding the use of {0:25} and {1:3}

[yang19177]

I was working through a book on machine learning and came across this snippet of code.

import mglearn 
import matplotlib.pyplot as plt 
import numpy as np
import pandas as pd

from sklearn.datasets import fetch_lfw_people 

people  = fetch_lfw_people(min_faces_per_person=20, resize = 0.7)
image_shape = people.images[0].shape 
counts = np.bincount(people.target)
for i, (count,name) in enumerate(zip(counts, people.target_names)):
    print("{0:25}  {1:3}".format(name, count), end='   ')
    if (i+1)% 3 == 0:
        print()

I'm not sure what is the use of {0:25} and {1:3} in the second last print function. I have not seen this before.
Thanks.

[snippsat]

I'm not sure what is the use of {0:25} and {1:3} in the second last print function

It's string formatting and the older version .format() that was new in Python 2.6.

name = 'Python forum'
count = 10
>>> print("{0:25}  {1:3}".format(name, count), end='   ')
Python forum                10  

With new f-string format new in Python 3.6,this is what you should use now.

>>> print(f"{name:25}{count:3}", end=' ')
Python forum              10 

So eg it's padding and aligning of strings,can play around with <>^

>>> print(f"{name:>14}{count:^20}")
  Python forum         10         
>>> print(f"{name:>20}{count:^5}")
        Python forum 10  
>>> print(f"{name:>20}{count:<5}")
        Python forum10 

>>> for word in 'f-strings are cool'.split():
...     print(f'{word.upper():~^20}')
...
~~~~~F-STRINGS~~~~~~
~~~~~~~~ARE~~~~~~~~~
~~~~~~~~COOL~~~~~~~~