第2章

Posted 2020-06-14

2-2：

（d）代码单独执行时，没有任何输出；在交互式解释器中执行会输出表达式的计算结果。

（e）

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

2-4：

（a）

#!/usr/bin/env python
inp = raw_input()
print inp

（b）

#!/usr/bin/env python
inp = int(raw_input())
print inp

2-5：

（a）

#!/usr/bin/python
a = 0
while a <= 10:
    print a
    a += 1

（b）

#!/usr/bin/env python
for item in range(11):
    print item

2-6:

固定数值：

#!/usr/bin/env python
num = ‘a‘
if type(num) in (int, float):
    if num < 0:
        print ‘num is less than 0‘
    elif num > 0:
        print ‘num is greater than 0‘
    else:
        print ‘num is equal to 0‘
else:
    print ‘invalid num‘

获取输入：

#!/usr/bin/env python
num = float(raw_input(‘Enter a number: ‘))
if num < 0:
    print ‘num is less than 0‘
elif num > 0:
    print ‘num is greater than 0‘
else:
    print ‘num is equal to 0‘

2-7：

while实现

#!/usr/bin/python
mystr = raw_input(‘Enter a string: ‘)
index = 0
while index < len(mystr):
    print mystr[index]
    index += 1

for实现

#!/usr/bin/python
myStr = raw_input(‘Enter a number: ‘)
for c in myStr:
    print c

2-8：

固定数值，while实现：

#!/usr/bin/env python
aList = [1,2,3,4,5]
index = 0
s = 0
while index < len(aList):
    s += aList[index]
    index += 1
print s

固定数值，for实现：

#!/usr/bin/env python
aList = [1,2,3,4,5]
s = 0
for item in aList:
    s += item
print s　　

用户输入，while实现：

#!/usr/bin/env python
a = 0
s = 0
while a < 5:
    s += int(raw_input(‘->‘))
    a += 1
print s

用户输入，for实现：

#!/usr/bin/env python
s = 0
print ‘Enter 5 numbers:‘
for i in range(5):
    s += int(raw_input(‘->‘))
print s

2-9：

#!/usr/bin/env python
aList = [1,2,5,6,7]
s = 0
for item in aList:
    s += item
ans = float(s) / len(aList)
print ans

2-10：

#!/usr/bin/env python
while True:
    num = float(raw_input(‘Enter a number between 1 and 100: ‘))
    if 1 < num < 100:
        print ‘succeed‘
        break
    else:
        print ‘the number is not between 1 and 100‘

2-11:

#!/usr/bin/env python
print ‘Enter 5 numbers:‘
s = 0
for i in range(5):
    s += float(raw_input(‘->‘))
while True:
    print ‘1. get the sum of 5 numbers‘
    print ‘2. get the avg of 5 numbers‘
    print ‘X. exit‘
    i = raw_input()
    if i == ‘1‘:
        print s
    elif i == ‘2‘:
        print s / 5
    elif i == ‘x‘ or i == ‘X‘:
        break

 2-12:

（a）键入dir()后出现：

[‘__builtins__‘, ‘__doc__‘, ‘__name__‘, ‘__package__‘]

打印各值的结果如下：

__guiltins__: <module ‘__builtin__‘ (built-in)>

__doc__: None

__name__: __main__

__package__: None

（b）返回信息如下：

<built-in function dir>

此信息表示dir是一个内建函数

（c）type(dir)的结果为：<type ‘builtin_function_or_method‘>

2-14:

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

2-15

（a）:

#!/usr/bin/env python
print ‘Please enter 3 numbers:‘
a = int(raw_input(‘->‘))
b = int(raw_input(‘->‘))
c = int(raw_input(‘->‘))
if a > b:
    a, b = b, a
if a > c:
    a, c = c, a
if b > c:
    b, c = c, b
print a, b, c

（b）:

#!/usr/bin/env python
print ‘Please enter 3 numbers:‘
a = int(raw_input(‘->‘))
b = int(raw_input(‘->‘))
c = int(raw_input(‘->‘))
if a > b:
    a, b = b, a
if a > c:
    a, c = c, a
if b > c:
    b, c = c, b
print c, b, a