python核心编程-习题-第二章

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'
>>>a
123
>>>b
'123'
>>>print a
123
>>>print b
123
>>>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 python
1 + 2 * 4

(e)使用print语句即可

2-3  略

2-4  (a)  

# -*- coding:utf-8 -*-
string = raw_input("Please enter something:")
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:123
Your enter is 123

 2-5  (a)

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

(b)

for i in range(11):
    print i

2-6  (1)

# -*- coding:utf-8 -*-
num = 10
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)

# -*- 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 = 0
while 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 = 0
sum = 0
while i < len(list1):
    sum = sum + list1[i]
    i += 1
print sum 

sum = 0
for 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 = 0
sum = 0
while i < len(list1):
    sum = sum + list1[i]
    i += 1
print sum 

sum = 0
for num in list1:
    sum = sum + num 
print sum 

2-9  

number = [12,345,67,890,123]
sum = 0
for num in number:
    sum = sum + num 
average = float(sum) / 5
print "%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"

2-12

（a）  dir()会显示所有全局变量

（b)   dir不加括号返回<built-in function dir>，对dir的基础介绍

（c)   type(dir)返回<type 'builtin_function_or_method'>,意思是内建的函数或方法

2-13

   

2-14

原语句：

print -2 * 4 + 3 ** 2

改写：

print -2 * 4 + (3 ** 2)

2-15/2-16    存疑，待补