实验1：答案

问题4

def falling(n, k):
    """Compute the falling factorial of n to depth k.

    >>> falling(6, 3)  # 6 * 5 * 4
    120
    >>> falling(4, 3)  # 4 * 3 * 2
    24
    >>> falling(4, 1)  # 4
    4
    >>> falling(4, 0)
    1
    """
    total, stop = 1, n-k
    while n > stop:
        total, n = total*n, n-1
    return total

问题5

def sum_digits(y):
    """Sum all the digits of y.

    >>> sum_digits(10) # 1 + 0 = 1
    1
    >>> sum_digits(4224) # 4 + 2 + 2 + 4 = 12
    12
    >>> sum_digits(1234567890)
    45
    >>> a = sum_digits(123) # make sure that you are using return rather than print
    >>> a
    6
    """
    total = 0
    while y > 0:
        total, y = total + y % 10, y // 10
    return total

问题7

def double_eights(n):
    """Return true if n has two eights in a row.
    >>> double_eights(8)
    False
    >>> double_eights(88)
    True
    >>> double_eights(2882)
    True
    >>> double_eights(880088)
    True
    >>> double_eights(12345)
    False
    >>> double_eights(80808080)
    False
    """
    prev_eight = False
    while n > 0:
        last_digit = n % 10
        if last_digit == 8 and prev_eight:
            return True
        elif last_digit == 8:
            prev_eight = True
        else:
            prev_eight = False
        n = n // 10
    return False