Lab 1: Variables & Functions, Control

Boolean Operators

This is because boolean operators, like arithmetic operators, have an order of operation:

• not has the highest priority
• and
• or has the lowest priority

Python values such as 0, None, '' (the empty string), and [] (the empty list) are considered false values. All other values are considered true values.

ZeroDivisionError：
1/0

WWPD:Control

>>> def xk(c, d):
...     if c == 4:
...         return 6
...     elif d >= 4:
...         return 6 + 7 + c
...     else:
...         return 25
>>> xk(10, 10)
23

>>> xk(10, 6)
23

>>> xk(4, 6)
6

>>> xk(0, 0)
25

>>> def how_big(x):
...     if x > 10:
...         print('huge')
...     elif x > 5:
...         return 'big'
...     elif x > 0:
...         print('small')
...     else:
...         print("nothin'")
>>> how_big(7)
'big'

>>> how_big(12)
huge

>>> how_big(1)
small

>>> how_big(-1)
nothin'

>>> n = 3
>>> while n >= 0:
...     n -= 1
...     print(n)
2
1
0
-1

>>> positive = 28
>>> while positive:
...    print("positive?")
...    positive -= 3
Infinite Loop

>>> positive = -9
>>> negative = -12
>>> while negative:
...    if positive:
...        print(negative)
...    positive += 3
...    negative += 3
-12
-9
-6

WWPD: Veritasiness

and和or计算规则：

1. 在纯and语句中，如果每一个表达式都为真，则返回最后一个真的值。如果有真有假，则返回第一个假的值。
2. 在纯or语句中，如果全假，返回最后一个假的值。如果有真有假，则返回第一个真的值。

>>> True and 13
13

>>> False or 0
0

>>> not 10
False

>>> not None
True

>>> True and 1 / 0 and False
Error

>>> True or 1 / 0 or False
True

>>> True and 0
0

>>> False or 1
1

>>> 1 and 3 and 6 and 10 and 15
15

>>> -1 and 1 > 0
True

>>> 0 or False or 2 or 1 / 0
2

>>> not 0
True

>>> (1 + 1) and 1
1

>>> 1/0 or True
Error

>>> (True or False) and False
False

Q4: Falling Factorial

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
    """
    "*** YOUR CODE HERE ***"
    if k == 0:
        return 1
    return reduce(mul, range(n, n-k, -1))

Q5: Sum Digits

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
"""
"*** YOUR CODE HERE ***"
ans = 0
while y:
    ans += y % 10
    y //=10
return ans

Q6: WWPD: What If?

>>> def ab(c, d):
...     if c > 5:
...         print(c)
...     elif c > 7:
...         print(d)
...     print('foo')
>>> ab(10, 20)
10
foo

__

>>> def bake(cake, make):
...     if cake == 0:
...         cake = cake + 1
...         print(cake)
...     if cake == 1:
...         print(make)
...     else:
...         return cake
...     return make
>>> bake(0, 29)
1
29
29

>>> bake(1, "mashed potatoes")
mashed potatoes
'mashed potatoes'

Q7: Double Eights

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
    """
    "*** YOUR CODE HERE ***"
    if n // 10 == 0:
        return False
    while n:
        last = n % 10
        n //= 10
        if last == 8 == (n % 10):
            return True
    return False