To convert a given number into a string that contains the base 2 representation of the number, with its sign.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 | ```
_nibbles = {"0":"0000", "1":"0001", "2":"0010", "3":"0011",
"4":"0100", "5":"0101", "6":"0110", "7":"0111",
"8":"1000", "9":"1001", "A":"1010", "B":"1011",
"C":"1100", "D":"1101", "E":"1110", "F":"1111",
"-":"-"}
def toBase2(number):
"""toBase2(number): given an int/long, converts it to
a string containing the number in base 2."""
# From a suggestion by Dennis Lee Bieber.
if number == 0:
return "0"
result = [_nibbles[nibble] for nibble in "%X"%number]
result[number<0] = result[number<0].lstrip("0")
return "".join(result)
# Small test:
for i in xrange(-20, 21):
print toBase2(i)
for i in xrange(-1000, 1000):
if i != int(toBase2(i),2):
print "Different"
``` |

This is the faster version that I've seen in pure Python, expecially for very long numbers. If Psyco is used, then for small numbers there is a different version (that uses bit shifts and an & 1) a bit faster than this one.

Tags: algorithms