Python 核心编程中文第二版课后练习 2.21 答案

2-2

(a) 计算 1 + 2 * 4

(b) 无输出

(c) 一样。无输出语句。

(d) 单独执行无输出，在交互解释器里执行输出结果。

(e)print 1 + 2 * 4

2-4

(a)

str = raw_input('input a str:')
print str

(b)

str = raw_input('input a int:')
print int(str)

2-5

(a)

i = 0
while i <= 10:
    print i,
    i += 1

(b)

for eachNum in range(11):
    print eachNum,

2-6

num = raw_input('input a num: ')
if num > 0:
    print '正数',
elif num < 0:
    print '负数',
else:
    print '0',

2-7

myStr = raw_input('input a str: ')
i = 0
while i < len(myStr):
    print myStr[i],
    i += 1

myStr = raw_input('input a str: ')
for c in myStr:
    print c,

2-8

aList = list()
for i in range(5):
    num = raw_input('input a num : ')
    aList.append(int(num))

i = 0
myNum = 0
while i < len(aList):
    myNum += aList[i]
    i += 1

print 'myNum is : %d' % (myNum)

2-9

aTuple = [ 1, 2, 3, 5, 6]
myNum = 0
for i in aTuple:
    myNum += i

print 'average value is : %f ' % (float(myNum) / len(aTuple))

2-10

b = bool(False)
while b is False:
    num = int(raw_input('input a num among 1 to 100 : '))
    if num >= 1 and num <= 100:
        print 'succeed!'
        break
    else:
        print 'input error!'

2-11

def display_menu():
    """展示菜单"""
    print '1. 取五个数的和'
    print '2. 取五个数的平均值'
    print 'x. 退出'
    sel = str(raw_input('输入您的选项：'))
    return sel

def tuple_sum(aTuple):
    """求和"""
    num = 0
    for i in aTuple:
        num += i
    return num

aTuple = (1, 2, 3, 4, 6)
while True :
    sel = display_menu()
    if sel == str('1'):
        print 'num is : %d ' % tuple_sum(aTuple)
    elif sel == str('2'):
        print 'average is : %f ' % (float(tuple_sum(aTuple))/len(aTuple))
    elif sel == str('x'):
        break
    else:
        continue

2-15

(a)

num1 = int(raw_input('input num1:'))
num2 = int(raw_input('input num2:'))
num3 = int(raw_input('input num3:'))
if num1 > num2:
    tmp = num2
    num2 = num1
    num1 = tmp
if num2 > num3:
    tmp = num3
    num3 = num2
    num2 = tmp
if num1 > num2:
    tmp = num2
    num2 = num1
    num1 = tmp

print 'min to max is %d, %d, %d' % (num1, num2, num3)

(b)

num1 = int(raw_input('input num1:'))
num2 = int(raw_input('input num2:'))
num3 = int(raw_input('input num3:'))
if num1 < num2:
    tmp = num2
    num2 = num1
    num1 = tmp
if num2 < num3:
    tmp = num3
    num3 = num2
    num2 = tmp
if num1 < num2:
    tmp = num2
    num2 = num1
    num1 = tmp

print 'min to max is %d, %d, %d' % (num1, num2, num3)

2-16

fobj = open('hello.txt', 'r')
for eachLine in fobj:
    print eachLine,
fobj.close()