Improve approx repr for better readability (#12665)

Adjust `ApproxScalar.__repr__` to format tolerances in decimal form for smaller ranges.

Closes #6985

---------

Co-authored-by: Bruno Oliveira <bruno@soliv.dev>
Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

Author: 3 people

changelog/6985.improvement.rst

@@ -0,0 +1,21 @@
+Improved :func:`pytest.approx` to enhance the readability of value ranges and tolerances between 0.001 and 1000.
+  * The `repr` method now provides clearer output for values within those ranges, making it easier to interpret the results.
+  * Previously, the output for those ranges of values and tolerances was displayed in scientific notation (e.g., `42 ± 1.0e+00`). The updated method now presents the tolerance as a decimal for better readability (e.g., `42 ± 1`).
+
+    Example:
+
+    **Previous Output:**
+
+    .. code-block:: console
+
+        >>> pytest.approx(42, abs=1)
+        42 ± 1.0e+00
+
+    **Current Output:**
+
+    .. code-block:: console
+
+        >>> pytest.approx(42, abs=1)
+        42 ± 1
+
+  -- by :user:`fazeelghafoor`

src/_pytest/python_api.py

@@ -406,7 +406,11 @@ def __repr__(self) -> str:
         # If a sensible tolerance can't be calculated, self.tolerance will
         # raise a ValueError.  In this case, display '???'.
         try:
-            vetted_tolerance = f"{self.tolerance:.1e}"
+            if 1e-3 <= self.tolerance < 1e3:
+                vetted_tolerance = f"{self.tolerance:n}"
+            else:
+                vetted_tolerance = f"{self.tolerance:.1e}"
+
             if (
                 isinstance(self.expected, Complex)
                 and self.expected.imag

testing/python/approx.py

@@ -92,6 +92,7 @@ def do_assert(lhs, rhs, expected_message, verbosity_level=0):
 
 SOME_FLOAT = r"[+-]?([0-9]*[.])?[0-9]+\s*"
 SOME_INT = r"[0-9]+\s*"
+SOME_TOLERANCE = rf"({SOME_FLOAT}|[+-]?[0-9]+(\.[0-9]+)?[eE][+-]?[0-9]+\s*)"
 
 
 class TestApprox:
@@ -103,7 +104,7 @@ def test_error_messages_native_dtypes(self, assert_approx_raises_regex):
                 "",
                 "  comparison failed",
                 f"  Obtained: {SOME_FLOAT}",
-                f"  Expected: {SOME_FLOAT} ± {SOME_FLOAT}",
+                f"  Expected: {SOME_FLOAT} ± {SOME_TOLERANCE}",
             ],
         )
 
@@ -119,9 +120,9 @@ def test_error_messages_native_dtypes(self, assert_approx_raises_regex):
                 r"  comparison failed. Mismatched elements: 2 / 3:",
                 rf"  Max absolute difference: {SOME_FLOAT}",
                 rf"  Max relative difference: {SOME_FLOAT}",
-                r"  Index \| Obtained\s+\| Expected           ",
-                rf"  a     \| {SOME_FLOAT} \| {SOME_FLOAT} ± {SOME_FLOAT}",
-                rf"  c     \| {SOME_FLOAT} \| {SOME_FLOAT} ± {SOME_FLOAT}",
+                r"  Index \| Obtained\s+\| Expected\s+",
+                rf"  a     \| {SOME_FLOAT} \| {SOME_FLOAT} ± {SOME_TOLERANCE}",
+                rf"  c     \| {SOME_FLOAT} \| {SOME_FLOAT} ± {SOME_TOLERANCE}",
             ],
         )
 
@@ -334,6 +335,11 @@ def test_repr_string(self):
             "approx({'b': 2.0 ± 2.0e-06, 'a': 1.0 ± 1.0e-06})",
         )
 
+        assert repr(approx(42, abs=1)) == "42 ± 1"
+        assert repr(approx(5, rel=0.01)) == "5 ± 0.05"
+        assert repr(approx(24000, abs=500)) == "24000 ± 500"
+        assert repr(approx(1500, abs=555)) == "1500 ± 555"
+
     def test_repr_complex_numbers(self):
         assert repr(approx(inf + 1j)) == "(inf+1j)"
         assert repr(approx(1.0j, rel=inf)) == "1j ± inf"
@@ -347,7 +353,7 @@ def test_repr_complex_numbers(self):
         assert repr(approx(3 + 4 * 1j)) == "(3+4j) ± 5.0e-06 ∠ ±180°"
 
         # absolute tolerance is not scaled
-        assert repr(approx(3.3 + 4.4 * 1j, abs=0.02)) == "(3.3+4.4j) ± 2.0e-02 ∠ ±180°"
+        assert repr(approx(3.3 + 4.4 * 1j, abs=0.02)) == "(3.3+4.4j) ± 0.02 ∠ ±180°"
 
     @pytest.mark.parametrize(
         "value, expected_repr_string",