python十进制转二进制，可指定位数
代码语言：javascript复制# 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> 
