核心编程答案（第六章）

例6.1

 import string


 def idcheck(myInput):
     alphas = string.letters + '-'
     nums = string.digits
     print 'Testees must be at least 2 chars long.'
     myInput = raw_input('Identifier to test:')
     if len(myInput) > 1:
         if myInput[0] not in alphas:
             print '''invalid: first symbol must be alphabetic'''
         else:
             for otherChar in myInput[1:]:
                 if otherChar not in alphas + nums:
                     print '''invalid: remaining symbol must be alphanumeric'
                     break
             print 'okay as an identifier'

备注：从性能上来讲，更少的操作可以减少时间，这里“if len(myInput) > 1:”每次都执行判断长度，可以一次性先赋值：stringlen = len(myInput)。这样就可以减少时间了。

 6-2

两个方法

str.find(sub[, start[, end]])

Return the lowest index in the string where substring sub is found, such that sub is contained in the slice s[start:end]. Optional arguments start and end are interpreted as in slice notation. Return -1 if sub is not found.

str.index(sub[, start[, end]])

Like find(), but raise ValueError when the substring is not found.

6-2

首先看下keyword具有的方法：

>>> import keyword
>>> dir(keyword)
['__all__', '__builtins__', '__doc__', '__file__', '__name__', '__package__', 'iskeyword', 'kwlist', 'main']

#!/usr/bin/env python
# encoding: utf-8
import string
import keyword


def idcheck(myInput):
    alphas = string.letters + '_'
    nums = string.digits
    if len(myInput) > 1:
        if myInput[0] not in alphas:
            print '''invalid: first symbol must be alphabetic'''
        elif keyword.iskeyword(myInput):
            print 'is keyword'
        else:
            for otherChar in myInput[1:]:
                if otherChar not in alphas + nums:
                    print '''invalid: remaining symbol must be alphanumeric'''
                    break
            print 'ok as an Identifier'
    else:
        if len(myInput) == 1:
            if myInput[0] not in alphas:
                print '''invalid: remaining symbol must be alphanumeric'''
            else:
                print 'ok as an Identifier'

if __name__ == "__main__":
    myInput = raw_input('Enter a string:')
    idcheck(myInput

 

6-8

这里没考虑为10开头的，还有几个地方显示不好的，比如100。

#!/usr/bin/env python
# encoding: utf-8

enlist = ["", "one", "two", "three", "four", "five", "six", "seven", "eight",
          "nine", "zero", "", "twenty", "thirty", "forty", "fifty", "sixty",
          "seventy", "eighty", "ninety", "zero", "one hundred", "two hundred",
          "three hundred", "four hundred", "five hundred", "six hundred",
          "seven hundred", "eight hundred", "nine hundred"]

num_str = raw_input('Enter a number: ')
numlen = len(num_str)
enexpress = ""
for i in range(numlen - 1, -1, -1):   # 从大到小
    enexpress = enexpress + "-" + enlist[int(num_str[numlen - 1 - i]) + 10 * i]   # 直接从列表中读出
enexpress = enexpress.strip("-")
print enexpress

 

6-10

#!/usr/bin/env python
# encoding: utf-8
import string


def Str_inverted(input_str):
    len_str = len(input_str)
    ch_str = ''
    for i in range(len_str):
        if input_str[i] in string.ascii_lowercase:
            ch_str = ch_str + input_str[i].upper()
        elif input_str[i] in string.ascii_uppercase:
            ch_str = ch_str + input_str[i].lower()
        else:
            ch_str = ch_str + input_str[i]
    return ch_str

if __name__ == "__main__":
    input_str = raw_input('enter a str: ')
    print Str_inverted(input_str)

另外，可以直接使用swapcase()，一步到位。所以要熟悉基本的函数方法标准库

 

6-11

思路：整数转换为二进制，八位二进制代表一位地址。

a、b

#!/usr/bin/env python
# encoding: utf-8
import ipdb


def int_ip(intnum):
    #  ipdb.set_trace()
    str_bin = bin(intnum)
    bin_len = len(str_bin)
    if 26 < bin_len <=34:  # 因为bin()前面会多出0b，所以要多出两位
        ip1 = str(eval(str_bin[:-24]))
        ip2 = str(eval('0b' + str_bin[-24:-16]))
        ip3 = str(eval('0b' + str_bin[-16:-8]))
        ip4 = str(eval('0b' + str_bin[-8:]))
        return ip1 + '.' + ip2 + '.' + ip3 + '.' + ip4
    elif 18 < bin_len <=26:
        ip1 = str('0')
        ip2 = str(eval(str_bin[:-16]))
        ip3 = str(eval('0b' + str_bin[-16:-8]))
        ip4 = str(eval('0b' + str_bin[-8:]))
        return ip1 + '.' + ip2 + '.' + ip3 + '.' + ip4
    elif 10 < bin_len <=18:
        ip1 = str('0')
        ip2 = str('0')
        ip3 = str(eval(str_bin[:-8]))
        ip4 = str(eval('0b' + str_bin[-8:]))
        return ip1 + '.' + ip2 + '.' + ip3 + '.' + ip4
    elif bin_len <=10:
        ip1 = str('0')
        ip2 = str('0')
        ip3 = str('0')
        ip4 = str(eval(str_bin))
        return ip1 + '.' + ip2 + '.' + ip3 + '.' + ip4
    else:
        return 'Out of range! '


def ip_to_int(ip_input):
    ipdb.set_trace()
    ip_list = ip_input.split('.')
    ip_int = int(ip_list[0]) * (256**3) + int(ip_list[1]) * (256 ** 2) + int(ip_list[2]) *256 + int(ip_list[3])
    return ip_int

if __name__ == "__main__":
    intnum = int(raw_input("Enter a int number: "))
    print int_ip(intnum)
    ip_input = raw_input('Enter ip: ')
    print ip_to_int(ip_input)

 

6-12

a、思路：先判断在不在里面，在的话，使用for来判定位置

def findchr(string, char):
    if char in string:
        strindex = []
        string_len = len(string)
        char_len = len(char)
        for i in range(string_len):
            if string[i:i + char_len] == char:
                strindex.append(i)
        return strindex
    else:
        return -1

if __name__ == "__main__":
    string = raw_input('Enter a string: ')
    char = raw_input('enter a char: ')
    print findchr(string, char)

6-14

思路：应用字典作全部例举，将输入直接作为键值，返回值。

import random


def Rochambeau(str_input):
    str_list = ['shitou', 'jiandao', 'bu']
    random_str = random.choice(str_list)
    cmp_dict = {'shitoujiandao': '1', 'shitoushitou': '0', 'shitoubu': '-1',
                'jiandaojiandao': '0', 'jiandaoshitou': '-1', 'jiandaobu': '1',
                'bujiandao': '-1', 'bushitou': '1', 'bubu': '0'}
    num_mean = {'1': 'you are win!', '0': 'draw!', '-1': 'you are losed!'}
    if str_input in str_list:
        cmp_str = str_input + random_str
        return "machin is '%s'" % random_str + '\n' + num_mean[cmp_dict[cmp_str]]
    else:
        return "please enter 'shihtou','jiandao','bu'"


if __name__ == "__main__":
    str_input = raw_input('Enter a string: ')
    print Rochambeau(str_input)