python核心編程-習題-第二章

PS:PDF在線地址：http://bcmi.sjtu.edu.cn/~zhaohai/ptm2012/data/Python-kernel.programming.v2.pdf

2-1  變量，print 和字符串格式化運算符。啓動交互式解釋器，給一些變量賦值（字符串，數值等等）並經過輸入變量名顯示它們的值。再用 print 語句作一樣的事。這兩者有何區別？ 也嘗試着使用字符串格式運算符%，多作幾回，慢慢熟悉。

# -*- coding:utf-8 -*-
>>>a = 123
>>>b = '123'
>>>a
123
>>>b
'123'
>>>print a
123
>>>print b
123
>>>print '儘管print語句輸出的a和b是同樣的，但他們仍然不同，a是%d,是整型；b是%s，是字符串。' % (a,b)
儘管print語句輸出的a和b是同樣的，但他們仍然不同，a是123,是整型；b是123，是字符串。

 

可見，在交互式解釋器中，經過輸入變量名稱顯示值是直接顯示各變量包含變量類型的值，即字符串帶有字符串的標誌''引號；經過print語句，則字符串引號''被去掉。

2-2  程序輸出

(a)  這段腳本用來計算 1 + 2 * 4 的值

(b)這段腳本保存後再運行不會輸出任何項

(c)保存爲腳本運行後，沒有任何輸出，與預想的同樣。究其緣由，是由於交互式解釋器和腳本運行的不一樣

(d)單獨執行這段代碼，不會有任何輸出；在交互式解釋器中輸入 1 + 2 * 4 ，會輸出"9".以下：

#!/usr/bin/env python
1 + 2 * 4

(e)使用print語句便可

2-3  略

2-4  (a)  

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

輸出：

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)

輸出：

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"它是正數！"
elif num < 0:
    print u"它是負數！"
else:
    print u"它是0"

(2)

# -*- coding:utf-8 -*-
num = int(raw_input("輸入一個數字：".decode("utf-8").encode("gbk")))
if num > 0:
    print u"它是正數！"
elif num < 0:
    print u"它是負數！"
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("請依次輸入五個數字：".decode("utf-8").encode("gbk")))
        sum = sum + num
        i += 1 
   
    return sum 
while True:
    choice = raw_input("1求和，2求平均數，X退出，請輸入你的選擇：".decode("utf-8").encode("gbk"))
    if choice == 'X':
        print u"程序將退出"
        break
    elif choice.isdigit() and int(choice) == 1:
    #isdigit()用來判斷一個對象是不是數字，是數字返回True，不然返回False。如123.isdigit()返回結果True
        print u"計算五個數的和"
        calc_sum()
        print u"這五個數的和是：",sum
        
    elif choice.isdigit() and int(choice) == 2:
        print u"計算五個數的平均值"
        calc_sum()
        print u"這五個數的平均值是：",float(sum) / 5
    else:
        print u"請從新輸入"

2-12

（a）  dir()會顯示全部全局變量

（b)   dir不加括號返回<built-in function dir>，對dir的基礎介紹

（c)   type(dir)返回<type 'builtin_function_or_method'>,意思是內建的函數或方法

2-13

   

2-14

原語句：

print -2 * 4 + 3 ** 2

改寫：

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

2-15/2-16    存疑，待補