Больше плохих "вводов"

Now that the from_roman() function works properly with good input, it's time to fit in the last piece of the puzzle: making it work properly with bad input. That means finding a way to look at a string and determine if it's a valid Roman numeral. This is inherently more difficult than validating numeric input in the to_roman() function, but you have a powerful tool at your disposal: regular expressions. (If you’re not familiar with regular expressions, now would be a good time to read the regular expressions chapter. ) As you saw in Case Study: Roman Numerals, there are several simple rules for constructing a Roman numeral, using the letters M, D, C, L, X, V, and I. Let's review the rules: 1. Sometimes characters are additive. I is 1, II is 2, and III is 3. VI is 6 (literally, “5 and 1”), VII is 7, and VIII is 8. 2. The tens characters (I, X, C, and M) can be repeated up to three times. At 4, you need to subtract from the next highest fives character. You can't represent 4 as IIII; instead, it is represented as IV (“1 less than 5”). 40 is written as XL (“10 less than 50”), 41 as XLI, 42 as XLII, 43 as XLIII, and then 44 as XLIV (“10 less than 50, then 1 less than 5”). 3. Sometimes characters are… the opposite of additive. By putting certain characters before others, you subtract from the final value. For example, at 9, you need to subtract from the next highest tens character: 8 is VIII, but 9 is IX (“1 less than 10”), not VIIII (since the I character can not be repeated four times). 90 is XC, 900 is CM. 4. The fives characters can not be repeated. 10 is always represented as X, never as VV. 100 is always C, never LL. 5. Roman numerals are read left to right, so the order of characters matters very much. DC is 600; CD is a completely different number (400, “100 less than 500”). CI is 101; IC is not even a valid Roman numeral (because you can't subtract 1 directly from 100; you would need to write it as XCIX, “10 less than 100, then 1 less than 10”). Thus, one useful test would be to ensure that the from_roman() function should fail when you pass it a string with too many repeated numerals. How many is “too many” depends on the numeral.

class FromRomanBadInput(unittest. TestCase):
def test_too_many_repeated_numerals(self):
'''from_roman should fail with too many repeated numerals'''
for s in ('MMMM', 'DD', 'CCCC', 'LL', 'XXXX', 'VV', 'IIII'):
self. assertRaises(roman6. InvalidRomanNumeralError, roman6. from_roman, s)

Another useful test would be to check that certain patterns aren’t repeated. For example, IX is 9, but IXIX is never valid.

def test_repeated_pairs(self):
'''from_roman should fail with repeated pairs of numerals'''
for s in ('CMCM', 'CDCD', 'XCXC', 'XLXL', 'IXIX', 'IVIV'):
self. assertRaises(roman6. InvalidRomanNumeralError, roman6. from_roman, s)

A third test could check that numerals appear in the correct order, from highest to lowest value. For example, CL is 150, but LC is never valid, because the numeral for 50 can never come before the numeral for 100. This test includes a randomly chosen set of invalid antecedents: I before M, V before X, and so on.

def test_malformed_antecedents(self):
'''from_roman should fail with malformed antecedents'''
for s in ('IIMXCC', 'VX', 'DCM', 'CMM', 'IXIV', 'MCMC', 'XCX', 'IVI', 'LM', 'LD', 'LC'):
self. assertRaises(roman6. InvalidRomanNumeralError, roman6. from_roman, s)

Each of these tests relies the from_roman() function raising a new exception, InvalidRomanNumeralError, which we haven’t defined yet.

def test_malformed_antecedents(self):
# roman6. py
class InvalidRomanNumeralError(ValueError): pass

All three of these tests should fail, since the from_roman() function doesn’t currently have any validity checking. (If they don’t fail now, then what the heck are they testing? )

you@localhost: ~/diveintopython3/examples$ python3 romantest6. py
FFF.......
======================================================================
FAIL: test_malformed_antecedents (__main__. FromRomanBadInput)
from_roman should fail with malformed antecedents
----------------------------------------------------------------------
Traceback (most recent call last):
File " romantest6. py", line 113, in test_malformed_antecedents
self. assertRaises(roman6. InvalidRomanNumeralError, roman6. from_roman, s)
AssertionError: InvalidRomanNumeralError not raised by from_roman
======================================================================
FAIL: test_repeated_pairs (__main__. FromRomanBadInput)
from_roman should fail with repeated pairs of numerals
----------------------------------------------------------------------
Traceback (most recent call last):
File " romantest6. py", line 107, in test_repeated_pairs
self. assertRaises(roman6. InvalidRomanNumeralError, roman6. from_roman, s)
AssertionError: InvalidRomanNumeralError not raised by from_roman
======================================================================
FAIL: test_too_many_repeated_numerals (__main__. FromRomanBadInput)
from_roman should fail with too many repeated numerals
----------------------------------------------------------------------
Traceback (most recent call last):
File " romantest6. py", line 102, in test_too_many_repeated_numerals
self. assertRaises(roman6. InvalidRomanNumeralError, roman6. from_roman, s)
AssertionError: InvalidRomanNumeralError not raised by from_roman
----------------------------------------------------------------------
Ran 10 tests in 0. 058s
FAILED (failures=3)

Good deal. Now, all we need to do is add the regular expression to test for valid Roman numerals into the from_roman() function.

CD

И опять тестируем...

you@localhost: ~/diveintopython3/examples$ python3 romantest7. py
..........
----------------------------------------------------------------------
Ran 10 tests in 0. 066s
OK

И премия за главное разочарование в этом году достается... я так волнуюсь... слову " ОК", выведенному как результат успешного прохождения теста.