How to format int to a bitstring of length n using format function in Python

Question

I am trying to convert an int to a binary string of length n using format function. I know how to do it for a fixed value of n, say n=3 and I want to convert integer 6 to a bitstring of length n=3, then I can do format(6, '03b').

May I know how to do the same for any given n? Clearly I cannot do format(6,'0nb'). So I'm wondering how to solve this?

Reopened. @q2w3e4, could you explain where you are stuck? Assign to the variable n and plug that variable into the second argument to format(). — Brad Solomon
– Brad Solomon, Commented Dec 29, 2020 at 13:16
@BradSolomon I don't know how to pass variable n to the second argument of format(). — q2w3e4
– q2w3e4, Commented Dec 29, 2020 at 13:18

Red · Accepted Answer · 2020-12-29 13:21:27Z

3

You can use a formatted string to dynamically insert the number n into the string:

n = 6
format(6, f'0{n}b')

answered Dec 29, 2020 at 13:21

Red

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rozumir · Accepted Answer · 2020-12-29 13:27:02Z

2

This answer is maybe a little misspoint but it use exact number of bit that are necessary to represent value, not a fixed value like format(x, f"{n}b"). Where x is some number, and n is number of bits.

import math

n = 6 # your number
format(n, f'0{int(math.log2(n))}b')

Here n is the number like x before, and there is no n, because we dynamicaly calculate right number of bits to repr n

edited Dec 29, 2020 at 13:27

answered Dec 29, 2020 at 13:20

rozumir

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1 Comment

cdlane Over a year ago

That seems a contorted way of doing format(n, f"0{n.bit_length()}b") and skip the import.

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