14.4.?roman.py, 第 4 階段 · Dive Into Python

# 14.4.?`roman.py`, 第 4 階段現在 `toRoman` 完成了，是開始編寫 `fromRoman` 的時候了。感謝那個將每個羅馬數字和對應整數關連的完美數據結構，這個工作不比 `toRoman` 函數復雜。 ## 例?14.9.?`roman4.py` 這個文件可以在例子目錄下的 `py/roman/stage4/` 目錄中找到。如果您還沒有下載本書附帶的樣例程序, 可以 [下載本程序和其他樣例程序](http://www.woodpecker.org.cn/diveintopython/download/diveintopython-exampleszh-cn-5.4b.zip "Download example scripts")。 ``` """Convert to and from Roman numerals""" #Define exceptions class RomanError(Exception): pass class OutOfRangeError(RomanError): pass class NotIntegerError(RomanError): pass class InvalidRomanNumeralError(RomanError): pass #Define digit mapping romanNumeralMap = (('M', 1000), ('CM', 900), ('D', 500), ('CD', 400), ('C', 100), ('XC', 90), ('L', 50), ('XL', 40), ('X', 10), ('IX', 9), ('V', 5), ('IV', 4), ('I', 1)) # toRoman function omitted for clarity (it hasn't changed) def fromRoman(s): """convert Roman numeral to integer""" result = 0 index = 0 for numeral, integer in romanNumeralMap: while s[index:index+len(numeral)] == numeral: result += integer index += len(numeral) return result ``` | | | | --- | --- | | \[1\] | 這和 [`toRoman`](stage_2.html#roman.stage2.example "例?14.3.?roman2.py") 的工作模式很相似。你遍歷整個羅馬數字數據結構 (一個元組的元組)，與前面不同的是不去一個個搜尋最大的整數，而是搜尋 “最大的”羅馬數字字符串。 | ## 例?14.10.?`fromRoman` 如何工作如果你不清楚 `fromRoman` 如何工作，在 `while` 結尾處添加一個 `print` 語句： ``` while s[index:index+len(numeral)] == numeral: result += integer index += len(numeral) print 'found', numeral, 'of length', len(numeral), ', adding', integer ``` ``` >>> import roman4 >>> roman4.fromRoman('MCMLXXII') found M , of length 1, adding 1000 found CM , of length 2, adding 900 found L , of length 1, adding 50 found X , of length 1, adding 10 found X , of length 1, adding 10 found I , of length 1, adding 1 found I , of length 1, adding 1 1972 ``` ## 例?14.11.?用 `romantest4.py` 測試 `roman4.py` 的結果 ``` fromRoman should only accept uppercase input ... FAIL toRoman should always return uppercase ... ok fromRoman should fail with malformed antecedents ... FAIL fromRoman should fail with repeated pairs of numerals ... FAIL fromRoman should fail with too many repeated numerals ... FAIL fromRoman should give known result with known input ... ok toRoman should give known result with known input ... ok fromRoman(toRoman(n))==n for all n ... ok toRoman should fail with non-integer input ... ok toRoman should fail with negative input ... ok toRoman should fail with large input ... ok toRoman should fail with 0 input ... ok ``` | | | | --- | --- | | \[1\] | 這兒有兩個令人激動的消息。一個是 `fromRoman` 對于所有有效輸入運轉正常，至少對于你測試的[已知值](testing_for_success.html#roman.testtoromanknownvalues.example "例?13.2.?testToRomanKnownValues")是這樣。 | | \[2\] | 第二個好消息是，[完備性測試](testing_for_sanity.html#roman.sanity.example "例?13.5.?以 toRoman 測試 fromRoman 的輸出")也通過了。與已知值測試的通過一起來看，你有理由相信 `toRoman` 和 `fromRoman` 對于所有有效輸入值工作正常。(尚不能完全相信，理論上存在這種可能性：`toRoman` 存在錯誤而導致一些特定輸入會產生錯誤的羅馬數字表示，_并且_ `fromRoman` 也存在相應的錯誤，把 `toRoman` 錯誤產生的這些羅馬數字錯誤地轉換為最初的整數。取決于你的應用程序和你的要求，你或許需要考慮這個可能性。如果是這樣，編寫更全面的測試用例直到解決這個問題。) | ``` ====================================================================== FAIL: fromRoman should only accept uppercase input ---------------------------------------------------------------------- Traceback (most recent call last): File "C:\docbook\dip\py\roman\stage4\romantest4.py", line 156, in testFromRomanCase roman4.fromRoman, numeral.lower()) File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises raise self.failureException, excName AssertionError: InvalidRomanNumeralError ====================================================================== FAIL: fromRoman should fail with malformed antecedents ---------------------------------------------------------------------- Traceback (most recent call last): File "C:\docbook\dip\py\roman\stage4\romantest4.py", line 133, in testMalformedAntecedent self.assertRaises(roman4.InvalidRomanNumeralError, roman4.fromRoman, s) File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises raise self.failureException, excName AssertionError: InvalidRomanNumeralError ====================================================================== FAIL: fromRoman should fail with repeated pairs of numerals ---------------------------------------------------------------------- Traceback (most recent call last): File "C:\docbook\dip\py\roman\stage4\romantest4.py", line 127, in testRepeatedPairs self.assertRaises(roman4.InvalidRomanNumeralError, roman4.fromRoman, s) File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises raise self.failureException, excName AssertionError: InvalidRomanNumeralError ====================================================================== FAIL: fromRoman should fail with too many repeated numerals ---------------------------------------------------------------------- Traceback (most recent call last): File "C:\docbook\dip\py\roman\stage4\romantest4.py", line 122, in testTooManyRepeatedNumerals self.assertRaises(roman4.InvalidRomanNumeralError, roman4.fromRoman, s) File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises raise self.failureException, excName AssertionError: InvalidRomanNumeralError ---------------------------------------------------------------------- Ran 12 tests in 1.222s FAILED (failures=4) ```