Google python course basic exercise——string2
在string1之后继续推出string2：
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1 # -*- coding: cp936 -*- 2 # D. verbing 3 # Given a string, if its length is at least 3, 4 # add 'ing' to its end. 5 # Unless it already ends in 'ing', in which case 6 # add 'ly' instead. 7 # If the string length is less than 3, leave it unchanged. 8 # Return the resulting string. 9 def verbing(s): 10 if len(s)>=3: 11 if s[-3:] == 'ing': 12 s = s + 'ly' 13 else: 14 s = s + 'ing' 15 return s 16 17 # E. not_bad 18 # Given a string, find the first appearance of the 19 # substring 'not' and 'bad'. If the 'bad' follows 20 # the 'not', replace the whole 'not'...'bad' substring 21 # with 'good'. 22 # Return the resulting string. 23 # So 'This dinner is not that bad!' yields: 24 # This dinner is good! 25 def not_bad(s): 26 if 'not' in s and 'bad' in s: #先判断有没有，如果去掉此句，则当s中没有not有bad时会出错 27 i = s.find('not') 28 j = s.find('bad') 29 if i<j: #强调首次出现时not在前，bad在后 30 s = s[0:i]+'good'+s[j+3:] #这样替换 31 return s 32 33 34 # F. front_back 35 # Consider dividing a string into two halves. 36 # If the length is even, the front and back halves are the same length. 37 # If the length is odd, we'll say that the extra char goes in the front half. 38 # e.g. 'abcde', the front half is 'abc', the back half 'de'. 39 # Given 2 strings, a and b, return a string of the form 40 # a-front + b-front + a-back + b-back 41 def front_back(a,b): 42 def front(s): #python支持函数嵌套 43 if (len(s)/2)*2 == len(s):#s的长度为偶数，也可以通过求余%实现 44 return s[0:len(s)/2] 45 else: 46 return s[0:len(s)/2+1] 47 def back(s): 48 if (len(s)/2)*2 == len(s): 49 return s[len(s)/2:] 50 else: 51 return s[len(s)/2+1:] 52 return front(a)+front(b)+back(a)+back(b) 53 54 # Simple provided test() function used in main() to print 55 # what each function returns vs. what it's supposed to return. 56 def test(got, expected): 57 if got == expected: 58 prefix = ' OK ' 59 else: 60 prefix = ' X ' 61 print '%s got: %s expected: %s' % (prefix, repr(got), repr(expected)) 62 63 # main() calls the above functions with interesting inputs, 64 # using the above test() to check if the result is correct or not. 65 def main(): 66 print 'verbing' 67 test(verbing('hail'), 'hailing') 68 test(verbing('swiming'), 'swimingly') 69 test(verbing('do'), 'do') 70 print 71 print 'not_bad' 72 test(not_bad('This movie is not so bad'), 'This movie is good') 73 test(not_bad('This dinner is not that bad!'), 'This dinner is good!') 74 test(not_bad('This tea is not hot'), 'This tea is not hot') 75 test(not_bad("It's bad yet not"), "It's bad yet not") 76 test(not_bad("It's bad yet not and bad"), "It's bad yet not and bad") 77 print 78 print 'front_back' 79 test(front_back('abcd', 'xy'), 'abxcdy') 80 test(front_back('abcde', 'xyz'), 'abcxydez') 81 test(front_back('Kitten', 'Donut'), 'KitDontenut') 82 if __name__ == '__main__': 83 main()
运行结果：
verbing OK got: 'hailing' expected: 'hailing' OK got: 'swimingly' expected: 'swimingly' OK got: 'do' expected: 'do' not_bad OK got: 'This movie is good' expected: 'This movie is good' OK got: 'This dinner is good!' expected: 'This dinner is good!' OK got: 'This tea is not hot' expected: 'This tea is not hot' OK got: "It's bad yet not" expected: "It's bad yet not" OK got: "It's bad yet not and bad" expected: "It's bad yet not and bad" front_back OK got: 'abxcdy' expected: 'abxcdy' OK got: 'abcxydez' expected: 'abcxydez' OK got: 'KitDontenut' expected: 'KitDontenut'
ps：
关于E项not_bad()函数：
- test(not_bad("It's bad yet not and bad"), "It's bad yet not and bad") 是我自己添加的测试项，检测not bad均为首次出现这一边界条件。
- 很容易想到的是利用正则表达式表达如下：
1 def not_bad(s): 2 import re 3 m = re.compile('not.*bad').search(s) 4 if m: 5 s = s[0:m.start()]+'good'+s[m.end():] 6 return s
正则表达式匹配原理类似于拿一个'not.*bad'的滑动窗口与串s进行匹配（注意不匹配换行符\n），所以对ps 1中的test测试结项是能找到匹配项的，运行结果如下：
not_bad OK got: 'This movie is good' expected: 'This movie is good' OK got: 'This dinner is good!' expected: 'This dinner is good!' OK got: 'This tea is not hot' expected: 'This tea is not hot' OK got: "It's bad yet not" expected: "It's bad yet not" X got: "It's bad yet good!" expected: "It's bad yet not and bad!"
