python-5 条件和递归

地板除 运算符(floor division operator) // 先做除法，然后将结果保留到整数。

>>> minutes = 105
>>> minutes / 60
1.75

>>> minutes = 105
>>> hours = minutes // 60
>>> hours
1

求余运算符 %。

布尔表达式：
5 == 5 = True
type(True) = <class 'bool'>

逻辑运算符：
and
or
not

条件语句if ：

if x > 0:
    print('x is positive')

# pass 语句
if x < 0:
    pass          # 待完成：需要处理负数值！

if x % 2 == 0:
    print('x is even')
else:
    print('x is odd')

# elif 
if x < y:
    print('x is less than y')
elif x > y:
    print('x is greater than y')
else:
    print('x and y are equal')

if 0 < x:
    if x < 10:
        print('x is a positive single-digit number.')

if 0 < x and x < 10:
    print('x is a positive single-digit number.')

if 0 < x < 10:
    print('x is a positive single-digit number.')

递归（recursion）。

键盘输入：
Python 提供了一个内建函数 input ，可以暂停程序运行，并等待用户输入。
在Python 2中，这个函数的名字叫raw_input。

>>> text = input()
What are you waiting for?
>>> text
What are you waiting for?

>>> name = input('What...is your name?\n')
What...is your name?
Arthur, King of the Britons!
>>> name
Arthur, King of the Britons!

>>> prompt = 'What...is the airspeed velocity of an unladen swallow?\n'
>>> speed = input(prompt)
What...is the airspeed velocity of an unladen swallow?
42
>>> int(speed)
42

循环：

def countdown(n):
    while n > 0:
        print(n)
        n = n - 1
    print('Blastoff!')

# break 语句 来跳出循环。
while True:
    line = input('> ')
    if line == 'done':
        break
    print(line)

print('Done!')

for i in range(4):
    print('Hello!')