python核心编程-习题-第二章

2019-11-14 17:02:36

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PS:PDF在线地址：http://bcmi.sjtu.edu.cn/~zhaohai/ptm2012/data/Python-kernel.PRogramming.v2.pdf

2-1 变量，print 和字符串格式化运算符。启动交互式解释器，给一些变量赋值（字符串，数值等等）并通过输入变量名显示它们的值。再用 print 语句做同样的事。这二者有何区别？也尝试着使用字符串格式运算符%，多做几次，慢慢熟悉。

# -*- coding:utf-8 -*->>>a = 123>>>b = '123'>>>a123>>>b'123'>>>print a123>>>print b123>>>print '尽管print语句输出的a和b是一样的，但他们仍然不一样，a是%d,是整型；b是%s，是字符串。' % (a,b)尽管print语句输出的a和b是一样的，但他们仍然不一样，a是123,是整型；b是123，是字符串。

可见，在交互式解释器中，通过输入变量名称显示值是直接显示各变量包含变量类型的值，即字符串带有字符串的标志''引号；通过print语句，则字符串引号''被去掉。

2-2 程序输出

(a) 这段脚本用来计算 1 + 2 * 4 的值

(b)这段脚本保存后再运行不会输出任何项

(c)保存为脚本运行后，没有任何输出，与预想的一样。究其原因，是因为交互式解释器和脚本运行的不同

(d)单独执行这段代码，不会有任何输出；在交互式解释器中输入 1 + 2 * 4 ，会输出"9".如下：

#!/usr/bin/env python1 + 2 * 4

(e)使用print语句即可

2-3 略

2-4 (a)

1 # -*- coding:utf-8 -*-2 string = raw_input("Please enter something:")3 print string

输出：

Please enter something:Python is number one!Python is number one!

(b)

# -*- coding:utf-8 -*-string = raw_input("Please enter a number:")print "Your enter is %d" % int(string)

输出：

Please enter a number:123Your enter is 123

2-5 (a)

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

(b)

for i in range(11):    print i

2-6 (1)

# -*- coding:utf-8 -*-num = 10if num > 0:    print u"它是正数！"elif num < 0:    print u"它是负数！"else:    print u"它是0"

(2)

# -*- coding:utf-8 -*-num = int(raw_input("输入一个数字：".decode("utf-8").encode("gbk")))if num > 0:    print u"它是正数！"elif num < 0:    print u"它是负数！"else:    print u"它是0"

2-7 (1) while

strings = raw_input("Please enter something:")i = 0while i < len(strings):    print strings[i],'(%d)' % i    i += 1

(2) for

strings = raw_input("Please enter something:")for i,string in enumerate(strings):    print string,"(%d)" % i

2-8

(1)

list1 = [123,45,678,91,124]i = 0sum = 0while i < len(list1):    sum = sum + list1[i]    i += 1print sum sum = 0for num in list1:    sum = sum + num print sum

(2)

num_one = int(raw_input("Please enter the first number:"))num_two = int(raw_input("Please enter the second numebr:"))num_three = int(raw_input("Please enter the third number:"))num_four = int(raw_input("Please enter the fourth number:"))num_five = int(raw_input("Please enter the fifth number:"))list1 = [num_one,num_two,num_three,num_four,num_five]i = 0sum = 0while i < len(list1):    sum = sum + list1[i]    i += 1print sum sum = 0for num in list1:    sum = sum + num print sum

2-9

number = [12,345,67,890,123]sum = 0for num in number:    sum = sum + num average = float(sum) / 5print "%f is the average of these five numbers." % average

2-10

while True:    num = int(raw_input("Please enter a number bewteen 1 and 100:"))    if num >= 1 and num <= 100:        print "Well Done.You done it."        break    else:        print "Man,you are wrong!Please learn to read the prompt!!!"        continue

2-11

# -*- coding:utf-8 -*-def calc_sum():    global sum     sum = 0    i = 0    while i < 5:        num = int(raw_input("请依次输入五个数字：".decode("utf-8").encode("gbk")))        sum = sum + num        i += 1        return sum while True:    choice = raw_input("1求和，2求平均数，X退出，请输入你的选择：".decode("utf-8").encode("gbk"))    if choice == 'X':        print u"程序将退出"        break    elif choice.isdigit() and int(choice) == 1:
    #isdigit()用来判断一个对象是否是数字，是数字返回True，否则返回False。如123.isdigit()返回结果True        print u"计算五个数的和"        calc_sum()        print u"这五个数的和是：",sum            elif choice.isdigit() and int(choice) == 2:        print u"计算五个数的平均值"        calc_sum()        print u"这五个数的平均值是：",float(sum) / 5    else:        print u"请重新输入"