## 14.2. roman.py, 第 2 阶段

### 例 14.3. roman2.py

```"""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))

def toRoman(n):
"""convert integer to Roman numeral"""
result = ""
for numeral, integer in romanNumeralMap:
while n >= integer:
result += numeral
n -= integer
return result

def fromRoman(s):
"""convert Roman numeral to integer"""
pass
```
 romanNumeralMap 是一个用来定义三个内容的元组的元组： 代表大部分罗马数字的字符。 注意不只是单字符的罗马数字，你同样在这里定义诸如 CM （“比一千少一百，即 900”）的双字符，这可以让稍后编写的 toRoman 简单一些。 罗马数字的顺序。他们是以降序排列的，从M 一路到 I。 每个罗马数字所对应的数值。 每个内部的元组都是一个 （numeral， value）数值对。 这里便显示出你丰富的数据结构带来的优势，你不需要什么特定的逻辑处理减法规则。你只需要通过搜寻 romanNumeralMap 寻找不大于输入数值的最大对应整数即可。 一旦找到，就在结果的结尾把这个整数对应的罗马字符添加到输出结果的末尾，从输入值中减去这个整数，一遍遍这样继续下去。

### 例 14.4. toRoman 如何工作

```        while n >= integer:
result += numeral
n -= integer
print 'subtracting', integer, 'from input, adding', numeral, 'to output'```
```>>> import roman2
>>> roman2.toRoman(1424)
subtracting 1000 from input, adding M to output
subtracting 400 from input, adding CD to output
subtracting 10 from input, adding X to output
subtracting 10 from input, adding X to output
subtracting 4 from input, adding IV to output
'MCDXXIV'
```

### 例 14.5. 以 romantest2.py 测试 roman2.py 的输出

```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 ... FAIL
toRoman should give known result with known input ... ok
fromRoman(toRoman(n))==n for all n ... FAIL
toRoman should fail with non-integer input ... FAIL
toRoman should fail with negative input ... FAIL
toRoman should fail with large input ... FAIL
toRoman should fail with 0 input ... FAIL```
 toRoman 通过，事实上其返回值总是大写的，因为 romanNumeralMap 定义的罗马字符都是以大写字母表示的。 因此这个测试已经通过了。 好消息来了：这个版本的 toRoman 函数能够通过 已知值测试。 记住，这并不能证明完全没问题，但至少通过测试多种有效输入考验了这个函数：包括每个单一字符的罗马数字，可能的最大输入（3999），以及可能的最长的罗马数字表示（3888 对应的） 。从这点来看，你有理由相信这个函数对于任何有效输入都不会出问题。 但是，函数还没办法 “处理” 无效输入，每个 无效输入测试 都失败了。这很好理解，因为你还没有对无效输入进行检查，测试用例希望捕捉到特定的异常（通过 assertRaises），而你根本没有让这些异常引发。 这是你下一阶段的工作。

```
======================================================================
FAIL: fromRoman should only accept uppercase input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage2\romantest2.py", line 156, in testFromRomanCase
roman2.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\stage2\romantest2.py", line 133, in testMalformedAntecedent
self.assertRaises(roman2.InvalidRomanNumeralError, roman2.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\stage2\romantest2.py", line 127, in testRepeatedPairs
self.assertRaises(roman2.InvalidRomanNumeralError, roman2.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\stage2\romantest2.py", line 122, in testTooManyRepeatedNumerals
self.assertRaises(roman2.InvalidRomanNumeralError, roman2.fromRoman, s)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: InvalidRomanNumeralError
======================================================================
FAIL: fromRoman should give known result with known input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage2\romantest2.py", line 99, in testFromRomanKnownValues
self.assertEqual(integer, result)
File "c:\python21\lib\unittest.py", line 273, in failUnlessEqual
raise self.failureException, (msg or '%s != %s' % (first, second))
AssertionError: 1 != None
======================================================================
FAIL: fromRoman(toRoman(n))==n for all n
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage2\romantest2.py", line 141, in testSanity
self.assertEqual(integer, result)
File "c:\python21\lib\unittest.py", line 273, in failUnlessEqual
raise self.failureException, (msg or '%s != %s' % (first, second))
AssertionError: 1 != None
======================================================================
FAIL: toRoman should fail with non-integer input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage2\romantest2.py", line 116, in testNonInteger
self.assertRaises(roman2.NotIntegerError, roman2.toRoman, 0.5)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: NotIntegerError
======================================================================
FAIL: toRoman should fail with negative input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage2\romantest2.py", line 112, in testNegative
self.assertRaises(roman2.OutOfRangeError, roman2.toRoman, -1)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: OutOfRangeError
======================================================================
FAIL: toRoman should fail with large input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage2\romantest2.py", line 104, in testTooLarge
self.assertRaises(roman2.OutOfRangeError, roman2.toRoman, 4000)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: OutOfRangeError
======================================================================
FAIL: toRoman should fail with 0 input
----------------------------------------------------------------------
Traceback (most recent call last):
File "C:\docbook\dip\py\roman\stage2\romantest2.py", line 108, in testZero
self.assertRaises(roman2.OutOfRangeError, roman2.toRoman, 0)
File "c:\python21\lib\unittest.py", line 266, in failUnlessRaises
raise self.failureException, excName
AssertionError: OutOfRangeError
----------------------------------------------------------------------
Ran 12 tests in 0.320s

FAILED (failures=10)```