I noticed that this question specifically asked about py.test. py.test 3.0 includes an approx()
function (well, really class) that is very useful for this purpose.
import pytest
assert 2.2 == pytest.approx(2.3)
# fails, default is ± 2.3e-06
assert 2.2 == pytest.approx(2.3, 0.1)
# passes
# also works the other way, in case you were worried:
assert pytest.approx(2.3, 0.1) == 2.2
# passes
The documentation is here.
You will have to specify what is "almost" for you:
assert abs(x-y) < 0.0001
to apply to tuples (or any sequence):
def almost_equal(x,y,threshold=0.0001):
return abs(x-y) < threshold
assert all(map(almost_equal, zip((1.32, 2.4), i_return_tuple_of_two_floats())
If you have access to NumPy it has great functions for floating point comparison that already do pairwise comparison with numpy.testing
.
Then you can do something like:
numpy.testing.assert_allclose(i_return_tuple_of_two_floats(), (1.32, 2.4))
These answers have been around for a long time, but I think the easiest and also most readable way is to use unittest for it's many nice assertions without using it for the testing structure.
(based on this answer)
import unittest
assertions = unittest.TestCase('__init__')
x = 0.00000001
assertions.assertAlmostEqual(x, 0) # pass
assertions.assertEqual(x, 0) # fail
# AssertionError: 1e-08 != 0
Just use * to unpack your return value without needing to introduce new names.
i_return_tuple_of_two_floats = lambda: (1.32, 2.4)
assertions.assertAlmostEqual(*i_return_tuple_of_two_floats()) # fail
# AssertionError: 1.32 != 2.4 within 7 places
Something like
assert round(x-y, 5) == 0
That is what unittest does
For the second part
assert all(round(x-y, 5) == 0 for x,y in zip((1.32, 2.4), i_return_tuple_of_two_floats()))
Probably better to wrap that in a function
def tuples_of_floats_are_almost_equal(X, Y):
return all(round(x-y, 5) == 0 for x,y in zip(X, Y))
assert tuples_of_floats_are_almost_equal((1.32, 2.4), i_return_tuple_of_two_floats())
If you want something that works not only with floats but for example Decimals you can use python's math.isclose():
# - rel_tol=0.01` is 1% difference tolerance.
assert math.isclose(actual_value, expected_value, rel_tol=0.01)
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