def bits_to_int(bits):
    total = 0
    pow2  = 1
    for bit in bits:
        total += bit * pow2
        pow2 *= 2
    return total

def int_to_bits(num):
    if num == 0:
        return [0]
    else:
        bits = []
        while num > 0:
            last_bit = num % 2
            bits.append(last_bit)
            num = num / 2
        return bits

def digits_to_int(digits, base):
    # 1. Remove the line below
    # 2. Copy the code from bits_to_int into this function
    # 3. Replace the 2s with base
    return 0

def int_to_digits(num, base):
    # 1. Remove the line below
    # 2. Copy the code from int_to_bits into this function
    # 3. Replace all the 2s with base
    return []

def bit_string_to_int(bit_string):
    # 0. Remove the line of code below!
    
    # 1. call list(bit_string), and put the result in a variable called
    #    bit_strings.
    #    bit_strings is a list of strings.  Each string is either '0' or '1'

    # 2. create another list, called bits, which will contain a list of ints
    #    either 0 or 1.  Initially, make that list empty : []

    # 3. write a for-loop which visits each string in bit_strings.
    #    each string should be converted into an int,
    #    and the result whould be appended to bits

    # 4. you will need to bits.reverse() , because the bits are backwards:
    #    the most significant bit should be LAST in the list, not FIRST.

    # 5. call bits_to_int(bits), and return its result.
    return 0

def pair_averages(numbers):
    # This function should compute the averages of pairs of numbers,
    # but it doesn't work correctly.
    for i in range(1, len(numbers)):
        numbers[i] = (numbers[i - 1] + numbers[i]) / 2
    return numbers


def main():
    print 'digits_to_int([1,2,3,0], 10)=',digits_to_int([1,2,3,0], 10)
    print 'int_to_digits(1230, 10)=',int_to_digits(1230, 10)
    print "bit_string_to_int('11011')=",bit_string_to_int('11011')
    print 'pair_averages([10,20,30,40])=',pair_averages([10,20,30,40])

if __name__ == '__main__':
    main()