python十進制轉二進制，可指定位數

# convert a decimal (denary, base 10) integer to a binary string (base 2)

tested with Python24   vegaseat    6/1/2005
def Denary2Binary(n):
    '''convert denary integer n to binary string bStr'''
    bStr = ''
    if n < 0:  raise ValueError, "must be a positive integer"
    if n == 0: return '0'
    while n > 0:
        bStr = str(n % 2) + bStr
        n = n >> 1
    return bStr
def int2bin(n, count=24):
    """returns the binary of integer n, using count number of digits"""
    return "".join([str((n >> y) & 1) for y in range(count-1, -1, -1)])
this test runs when used as a standalone program, but not as an imported module
let's say you save this module as den2bin.py and use it in another program
when you import den2bin the name namespace would now be  den2bin  and the
test would be ignored
if name == 'main':
    print Denary2Binary(255)  # 11111111

# convert back to test it
print int(Denary2Binary(255), 2)  # 255

print

# this version formats the binary
print int2bin(255, 12)  # 000011111111
# test it
print int("000011111111", 2)  # 255

print

# check the exceptions
print Denary2Binary(0)
print Denary2Binary(-5)  # should give a ValueError</pre>