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diff: support for inf/-inf #150

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diff: support for inf/-inf #150

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e1d627d
Fix are_different check for infs
eric-bonfadini Feb 9, 2021
6b897b7
Fixed pycodestyle issue
eric-bonfadini Feb 9, 2021
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9 changes: 9 additions & 0 deletions dictdiffer/utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -264,10 +264,19 @@ def are_different(first, second, tolerance):
return False

first_is_nan, second_is_nan = bool(first != first), bool(second != second)
first_is_inf, second_is_inf = first == float('inf'), second == float('inf')
first_is_ninf = first == float('-inf')
second_is_ninf = second == float('-inf')

if first_is_nan or second_is_nan:
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@joesolly joesolly Mar 31, 2021

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on a more mathematical level, should two nan or two inf or two -inf be considered the same? It is improbable that two inf are the same when you are running a diff. If we agree that they should be considered the same, then this all looks great!

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@eric-bonfadini eric-bonfadini Apr 15, 2021

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I asked myself the same question while doing this PR and I found links like this stating that inf==inf and -inf==-inf .

On the contrary, it seems that they agree that Nan!=Nan , but that's outside the scope of this PR.

Let me know if you prefer not considering two inf the same, I can easily adapt tests and code.

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@joesolly joesolly Apr 15, 2021

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I think following convention is preferred over mathematical precision, so this sounds good to me 👍

# two 'NaN' values are not different (see issue #114)
return not (first_is_nan and second_is_nan)
if first_is_inf or second_is_inf:
# two 'inf' values are not different
return not (first_is_inf and second_is_inf)
if first_is_ninf or second_is_ninf:
# two '-inf' values are not different
return not (first_is_ninf and second_is_ninf)
elif isinstance(first, num_types) and isinstance(second, num_types):
# two numerical values are compared with tolerance
return abs(first-second) > tolerance * max(abs(first), abs(second))
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29 changes: 29 additions & 0 deletions tests/test_dictdiffer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -277,6 +277,35 @@ def test_numpy_nan(self):
result = list(diff(first, second))
assert result == []

def test_inf(self):
first = {'a': [1.0, 2.0, 3.0, 4.0]}
second = {'a': [1.0, 2.0, 3.0, float('inf')]}
diffed = next(diff(first, second))
assert ('change', ['a', 3], (4, float('inf'))) == diffed

first = {'a': [1.0, 2.0, 3.0, 4.0]}
second = {'a': [1.0, 2.0, 3.0, float('-inf')]}
diffed = next(diff(first, second))
assert ('change', ['a', 3], (4, float('-inf'))) == diffed

first = {'a': [1.0, 2.0, 3.0, float('inf')]}
second = {'a': [1.0, 2.0, 3.0, float('inf')]}
result = list(diff(first, second))
assert result == []

first = {'a': [1.0, 2.0, 3.0, float('inf')]}
second = {'a': [1.0, 2.0, 3.0, float('-inf')]}
diffed = next(diff(first, second))
assert ('change', ['a', 3], (float('inf'), float('-inf'))) == diffed

@unittest.skipIf(not HAS_NUMPY, 'NumPy is not installed')
def test_numpy_inf(self):
import numpy as np
first = {'a': [1.0, 2.0, 3.0, 4.0]}
second = {'a': [1.0, 2.0, 3.0, np.float64('inf')]}
diffed = next(diff(first, second))
assert ('change', ['a', 3], (4, np.float64('inf'))) == diffed

def test_unicode_keys(self):
first = {u'привет': 1}
second = {'hello': 1}
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