python_api: let approx() take nonnumeric values

AUTHORS

@@ -129,6 +129,7 @@ Ilya Konstantinov
 Ionuț Turturică
 Iwan Briquemont
 Jaap Broekhuizen
+Jakob van Santen
 Jakub Mitoraj
 Jan Balster
 Janne Vanhala

changelog/7710.improvement.rst

@@ -0,0 +1,3 @@
+Use strict equality comparison for nonnumeric types in ``approx`` instead of
+raising ``TypeError``.
+This was the undocumented behavior before 3.7, but is now officially a supported feature.

src/_pytest/python_api.py

@@ -4,7 +4,7 @@
 from collections.abc import Mapping
 from collections.abc import Sized
 from decimal import Decimal
-from numbers import Number
+from numbers import Complex
 from types import TracebackType
 from typing import Any
 from typing import Callable
@@ -145,7 +145,10 @@ def __repr__(self) -> str:
         )
 
     def __eq__(self, actual) -> bool:
-        if set(actual.keys()) != set(self.expected.keys()):
+        try:
+            if set(actual.keys()) != set(self.expected.keys()):
+                return False
+        except AttributeError:
             return False
 
         return ApproxBase.__eq__(self, actual)
@@ -160,8 +163,6 @@ def _check_type(self) -> None:
             if isinstance(value, type(self.expected)):
                 msg = "pytest.approx() does not support nested dictionaries: key={!r} value={!r}\n  full mapping={}"
                 raise TypeError(msg.format(key, value, pprint.pformat(self.expected)))
-            elif not isinstance(value, Number):
-                raise _non_numeric_type_error(self.expected, at="key={!r}".format(key))
 
 
 class ApproxSequencelike(ApproxBase):
@@ -176,7 +177,10 @@ def __repr__(self) -> str:
         )
 
     def __eq__(self, actual) -> bool:
-        if len(actual) != len(self.expected):
+        try:
+            if len(actual) != len(self.expected):
+                return False
+        except TypeError:
             return False
         return ApproxBase.__eq__(self, actual)
 
@@ -189,10 +193,6 @@ def _check_type(self) -> None:
             if isinstance(x, type(self.expected)):
                 msg = "pytest.approx() does not support nested data structures: {!r} at index {}\n  full sequence: {}"
                 raise TypeError(msg.format(x, index, pprint.pformat(self.expected)))
-            elif not isinstance(x, Number):
-                raise _non_numeric_type_error(
-                    self.expected, at="index {}".format(index)
-                )
 
 
 class ApproxScalar(ApproxBase):
@@ -210,16 +210,23 @@ def __repr__(self) -> str:
         For example, ``1.0 ± 1e-6``, ``(3+4j) ± 5e-6 ∠ ±180°``.
         """
 
-        # Infinities aren't compared using tolerances, so don't show a
-        # tolerance. Need to call abs to handle complex numbers, e.g. (inf + 1j).
-        if math.isinf(abs(self.expected)):
+        # Don't show a tolerance for values that aren't compared using
+        # tolerances, i.e. non-numerics and infinities. Need to call abs to
+        # handle complex numbers, e.g. (inf + 1j).
+        if (not isinstance(self.expected, (Complex, Decimal))) or math.isinf(
+            abs(self.expected)
+        ):
             return str(self.expected)
 
         # If a sensible tolerance can't be calculated, self.tolerance will
         # raise a ValueError.  In this case, display '???'.
         try:
             vetted_tolerance = "{:.1e}".format(self.tolerance)
-            if isinstance(self.expected, complex) and not math.isinf(self.tolerance):
+            if (
+                isinstance(self.expected, Complex)
+                and self.expected.imag
+                and not math.isinf(self.tolerance)
+            ):
                 vetted_tolerance += " ∠ ±180°"
         except ValueError:
             vetted_tolerance = "???"
@@ -238,6 +245,15 @@ def __eq__(self, actual) -> bool:
         if actual == self.expected:
             return True
 
+        # If either type is non-numeric, fall back to strict equality.
+        # NB: we need Complex, rather than just Number, to ensure that __abs__,
+        # __sub__, and __float__ are defined.
+        if not (
+            isinstance(self.expected, (Complex, Decimal))
+            and isinstance(actual, (Complex, Decimal))
+        ):
+            return False
+
         # Allow the user to control whether NaNs are considered equal to each
         # other or not.  The abs() calls are for compatibility with complex
         # numbers.
@@ -408,6 +424,18 @@ def approx(expected, rel=None, abs=None, nan_ok: bool = False) -> ApproxBase:
         >>> 1 + 1e-8 == approx(1, rel=1e-6, abs=1e-12)
         True
 
+    You can also use ``approx`` to compare nonnumeric types, or dicts and
+    sequences containing nonnumeric types, in which case it falls back to
+    strict equality. This can be useful for comparing dicts and sequences that
+    can contain optional values::
+
+        >>> {"required": 1.0000005, "optional": None} == approx({"required": 1, "optional": None})
+        True
+        >>> [None, 1.0000005] == approx([None,1])
+        True
+        >>> ["foo", 1.0000005] == approx([None,1])
+        False
+
     If you're thinking about using ``approx``, then you might want to know how
     it compares to other good ways of comparing floating-point numbers.  All of
     these algorithms are based on relative and absolute tolerances and should
@@ -465,6 +493,14 @@ def approx(expected, rel=None, abs=None, nan_ok: bool = False) -> ApproxBase:
        follows a fixed behavior. `More information...`__
 
        __ https://docs.python.org/3/reference/datamodel.html#object.__ge__
+
+    .. versionchanged:: 3.7.1
+       ``approx`` raises ``TypeError`` when it encounters a dict value or
+       sequence element of nonnumeric type.
+
+    .. versionchanged:: 6.1.0
+       ``approx`` falls back to strict equality for nonnumeric types instead
+       of raising ``TypeError``.
     """
 
     # Delegate the comparison to a class that knows how to deal with the type
@@ -486,8 +522,6 @@ def approx(expected, rel=None, abs=None, nan_ok: bool = False) -> ApproxBase:
 
     if isinstance(expected, Decimal):
         cls = ApproxDecimal  # type: Type[ApproxBase]
-    elif isinstance(expected, Number):
-        cls = ApproxScalar
     elif isinstance(expected, Mapping):
         cls = ApproxMapping
     elif _is_numpy_array(expected):
@@ -500,7 +534,7 @@ def approx(expected, rel=None, abs=None, nan_ok: bool = False) -> ApproxBase:
     ):
         cls = ApproxSequencelike
     else:
-        raise _non_numeric_type_error(expected, at=None)
+        cls = ApproxScalar
 
     return cls(expected, rel, abs, nan_ok)
 

testing/python/approx.py

@@ -1,4 +1,5 @@
 import operator
+import sys
 from decimal import Decimal
 from fractions import Fraction
 from operator import eq
@@ -329,6 +330,9 @@ def test_tuple_wrong_len(self):
         assert (1, 2) != approx((1,))
         assert (1, 2) != approx((1, 2, 3))
 
+    def test_tuple_vs_other(self):
+        assert 1 != approx((1,))
+
     def test_dict(self):
         actual = {"a": 1 + 1e-7, "b": 2 + 1e-8}
         # Dictionaries became ordered in python3.6, so switch up the order here
@@ -346,6 +350,13 @@ def test_dict_wrong_len(self):
         assert {"a": 1, "b": 2} != approx({"a": 1, "c": 2})
         assert {"a": 1, "b": 2} != approx({"a": 1, "b": 2, "c": 3})
 
+    def test_dict_nonnumeric(self):
+        assert {"a": 1.0, "b": None} == pytest.approx({"a": 1.0, "b": None})
+        assert {"a": 1.0, "b": 1} != pytest.approx({"a": 1.0, "b": None})
+
+    def test_dict_vs_other(self):
+        assert 1 != approx({"a": 0})
+
     def test_numpy_array(self):
         np = pytest.importorskip("numpy")
 
@@ -463,20 +474,67 @@ def test_foo():
             ["*At index 0 diff: 3 != 4 ± {}".format(expected), "=* 1 failed in *="]
         )
 
+    @pytest.mark.parametrize(
+        "x, name",
+        [
+            pytest.param([[1]], "data structures", id="nested-list"),
+            pytest.param({"key": {"key": 1}}, "dictionaries", id="nested-dict"),
+        ],
+    )
+    def test_expected_value_type_error(self, x, name):
+        with pytest.raises(
+            TypeError,
+            match=r"pytest.approx\(\) does not support nested {}:".format(name),
+        ):
+            approx(x)
+
     @pytest.mark.parametrize(
         "x",
         [
             pytest.param(None),
             pytest.param("string"),
             pytest.param(["string"], id="nested-str"),
-            pytest.param([[1]], id="nested-list"),
             pytest.param({"key": "string"}, id="dict-with-string"),
-            pytest.param({"key": {"key": 1}}, id="nested-dict"),
         ],
     )
-    def test_expected_value_type_error(self, x):
-        with pytest.raises(TypeError):
-            approx(x)
+    def test_nonnumeric_okay_if_equal(self, x):
+        assert x == approx(x)
+
+    @pytest.mark.parametrize(
+        "x",
+        [
+            pytest.param("string"),
+            pytest.param(["string"], id="nested-str"),
+            pytest.param({"key": "string"}, id="dict-with-string"),
+        ],
+    )
+    def test_nonnumeric_false_if_unequal(self, x):
+        """For nonnumeric types, x != pytest.approx(y) reduces to x != y"""
+        assert "ab" != approx("abc")
+        assert ["ab"] != approx(["abc"])
+        # in particular, both of these should return False
+        assert {"a": 1.0} != approx({"a": None})
+        assert {"a": None} != approx({"a": 1.0})
+
+        assert 1.0 != approx(None)
+        assert None != approx(1.0)  # noqa: E711
+
+        assert 1.0 != approx([None])
+        assert None != approx([1.0])  # noqa: E711
+
+    @pytest.mark.skipif(sys.version_info < (3, 7), reason="requires ordered dicts")
+    def test_nonnumeric_dict_repr(self):
+        """Dicts with non-numerics and infinites have no tolerances"""
+        x1 = {"foo": 1.0000005, "bar": None, "foobar": inf}
+        assert (
+            repr(approx(x1))
+            == "approx({'foo': 1.0000005 ± 1.0e-06, 'bar': None, 'foobar': inf})"
+        )
+
+    def test_nonnumeric_list_repr(self):
+        """Lists with non-numerics and infinites have no tolerances"""
+        x1 = [1.0000005, None, inf]
+        assert repr(approx(x1)) == "approx([1.0000005 ± 1.0e-06, None, inf])"
 
     @pytest.mark.parametrize(
         "op",