Converting a decimal integer (denary, base 10) to a binary string (base 2) is amazingly simple. An exception is raised for negative numbers and zero is a special case. To test the result, the binary string is converted back to the decimal value, easily done with the int(bStr, 2) function.
# 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
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