This is just one of many possible solutions:
original = int(input('Please enter a number between 0 and 31: '))
number = original
bit_value = 32
cards = ''
while bit_value > 1:
bit_value = bit_value / 2
if number >= bit_value:
cards = cards + 'W'
number = number - bit_value
else:
cards = cards + 'B'
print('The binary representation for the number ' + str(original) + ' is ' + str(cards))