On 30/10/2010 02:41, Steven D'Aprano wrote:
Raymond Hettinger wrote:
The API for the unittest module has grown fat (the documentation
is approaching 2,000 lines and 10,000 words like a small book). I
think we can improve learnability by focusing on the most important
parts of the API.
I would like to simplify and clean-up the API for the unittest module
by de-documenting assertSetEqual(), assertDictEqual(),
assertListEqual, and assertTupleEqual().
While you're at it, what do you think of assertAlmostEqual? Is there a
use-case for it as it exists now?
As I see it, it suffers from a number of problems:
(1) Comparing floats for equality to some number of decimal places is
rarely (never?) the right way to do it. Comparison to some number of
significant figures would be better. Specifying an absolute or
relative error would be better still.
I agree, comparing floats to a specific number of decimal places has
almost always been useless to me. What would be nice would be a 'delta'
keyword argument allowing you to specify a difference instead. That
could also allow you to compare non-numeric objects like times as well.
Now where are the keys to that time machine...
http://docs.python.org/dev/library/unittest.html#unittest.TestCase.assertAlmostEqual
All the best,
Michael Foord
(2) This leads people to write the wrong test, because
assertAlmostEqual exists and is easy to use, while the right test is
tricky and requires better understanding of floating point issues.
Example: I recently wrote tests using assertAlmostEqual where I
specified places=12, because my code should have been accurate to 12
significant figures. Worked fine for small floating point, but when I
started testing values of the order of 10000, my tests started
failing, because although it was correct to > 12 significant figures,
five of those figures were not decimal places.
(3) In the rare case that mere rounding is the right way to compare
for approximate equality, assertAlmostEqual doesn't save you much: a
handful of characters, that's about all.
self.assertAlmostEqual(x, y, places=n)
vs.
self.assertEqual(round(x, n), round(y, n))
(Specifying the number of decimal places is keyword-only in 3.1. To
me, that seems to be a gratuitous change from 2.x, where it could be
specified as a positional argument.)
--
http://www.voidspace.org.uk/
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