Python: Choose number of bits to represent binary number

Question

I am curious as to how I can change the number of bits to represent a binary number. For example, say I want express decimal 1 to binary. I use:

bin(1) and get 0b1.

How can I get the return to say 0b01 or 0b001 or 0b0001 etc?

Answer 1

Use the Format String Syntax:

>>> format(1, '#04b')
'0b01'
>>> format(1, '#05b')
'0b001'
>>> format(1, '#06b')
'0b0001'

Answer 2

You can use str.zfill to pad the binary part:

def padded_bin(i, width):
    s = bin(i)
    return s[:2] + s[2:].zfill(width)

Answer 3

I don't believe there's a builtin way to do this. However, since bin just returns a string, you could write a wrapper function which modifies the string to have the right number of bits:

def binbits(x, n):
    """Return binary representation of x with at least n bits"""
    bits = bin(x).split('b')[1]

    if len(bits) < n:
        return '0b' + '0' * (n - len(bits)) + bits
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