def bs(s):
    return str(s) if s<=1 else bs(s>>1) + str(s&1)

Couldn't find a built in way to do this.  Neatly prints an int as bit string.  Recursive so not the most efficient but switching it to iterative would be cake if performance is that big an issue.  Warning doesn't support negative numbers... simple enough to convert to one or two's complement.

Convert from int to bit string

Python