python系列(2) 函数

3.1 def语句与参数

def hello(name):
    print('Hello' +' ' +  name)
hello('Alice')
hello('Bob')

3.2 返回值和return语句

import random
def getAnswer(answerNumber):
    if answerNumber == 1:
        return 'It is a certain'
    elif answerNumber == 2:
        return 'Yes'
    elif answerNumber == 3:
        return 'It is decidely so'
    elif answerNumber == 4:
        return 'Reply hazy try again '
    elif answerNumber == 5:
        return 'Ask again later'
    elif answerNumber == 6:
        return 'Concentrate and ask again'
    elif answerNumber == 7:
        return 'My replly is no'
    elif answerNumber == 8:
        return 'Out look not so good'
    elif answerNumber == 9:
        return 'Very doubtful'
r = random.randint(1, 9)
fortune = getAnswer(r)
print(fortune)

3.3 global语句

如果需要在一个函数内修改全局变量，就会使用global语句。如果在函数的顶部有global eggs语句，就告诉python，eggs指代全局变量，所以不要用这个名字
创建局部变量

def spam():
    global eggs
    eggs = 'spam'
eggs = 'global'
spam()
print(eggs)

3.4 一个小程序，猜数字

import random
secretNumber = random.randint(1, 20)
print('I am thinkinng of a number between 1 and 20')
# ask the player too guess 6 times
for guessesTaken in range(1, 7):
    print('Take a guess')
    guess = int(input())
    if guess < secretNumber:
        print('Your guess is too low')
    elif guess > secretNumber:
        print('Your guess is too high')
    else:
        break # this condition is the coorrect guess
if guess == secretNumber:
    print('Good job! your guessd my number in' + str(guessesTaken) + 'guesses!')
else:
    print('Nope, The number I was thinking of was' + str(secretNumber))

实践项目

编写一个名为collatz()的函数，他有一个名为number的参数，如果参数是偶数，那么collatz()就打印出number//2,并返回该值，如果Number是奇数，collatz()
就打印并返回 3*number + 1
然后编写一个程序，让用户输入一个整数，并不断对这个数调用collatz(),直到函数返回值为1

def collatz(number):
    if number % 2 == 0:
        return a//2
    elif number % 2 !=0:
        return  3 * a + 1
try:
    a = int(input('please input a number'))
    while True:
        a = collatz(a)
        if a ==  1:
            print(a)
            break
except ValueError:
    print('Please input a right int num')