need help in understanding a code

Question

Can anyone explain this code a little. I can't understand what n does here? We already have taken N = int(input()) as input then why n=len(bin(N))-2 ? I couldn't figure it out.

N = int(input())
n = len(bin(N))-2
for i in range(1,N+1):
    print(str(i).rjust(n) + " " + format(i,'o').rjust(n) + " " + format(i,'X').rjust(n) + " " + format(i,'b').rjust(n))

Answer 1

n counts the number of bits in the number N . bin() produces the binary representation (zeros and ones), as as string with the 0b prefix:

>>> bin(42)
'0b101010'

so len(bin(n)) takes the length of that output string, minus 2 to account for the prefix.

See the bin() documentation :

Convert an integer number to a binary string prefixed with “0b”.

The length is used to set the width of the columns (via str.rjust() , which adds spaces to the front of a string to create an output n characters wide). Knowing how many characters the widest binary representation needs is helpful here.

However, the same information can be gotten directly from the number, with the int.bitlength() method :

>>> N = 42
>>> N.bit_length()
6
>>> len(bin(N)) - 2
6

The other columns are also oversized for the numbers. You could instead calculate max widths for each column, and use str.format() or an f-string to do the formatting:

from math import log10

N = int(input())
decwidth = int(log10(N) + 1)
binwidth = N.bit_length()
hexwidth = (binwidth - 1) // 4 + 1
octwidth = (binwidth - 1) // 3 + 1

for i in range(1, N + 1):
    print(f'{i:>{decwidth}d} {i:>{octwidth}o} {i:>{hexwidth}X} {i:>{binwidth}b}')