python十进制转二进制，可指定位数详解编程语言

python十进制转二进制，可指定位数

# 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