[Python-Dev] Optional delta argument for assertAlmostEqual
fuzzyman at voidspace.org.uk
Sat Mar 27 01:59:21 CET 2010
A user has suggested an optional argument to
unittest.TestCase.assertAlmostEqual for specifying a maximum difference
between the expected and actual values, instead of using rounding.
This sounds great to me as the default implementation of
assertAlmostEqual has *never* been useful to me (YMMV). In fact one of
the first things I do on setting up a test suite is provide a TestCase
that overrides assertAlmostEqual with an implementation that uses a
delta rather than rounding.
The implementation would be effectively:
assert abs(actual - expected) < delta
This has the advantage that it allows things like:
The issue is this would make the signature of assertAlmostEqual (and its
def assertAlmostEqual(self, first, second, places=7, msg=None, delta=None)
Note that delta comes after msg, which is different to other assert
methods. To put delta before msg would be backwards incompatible with
existing uses passing arguments positionally. In Python 3.2 we can make
delta a keyword argument. Passing both places and delta would be an
Anyway, unless there are strenuous objections I intend to do this.
All the best,
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