Failed doctest test for decimal.Decimal.__round__

[serhiy-storchaka]

Bug report

Bug description:

$ ./python -m test -v test_decimal -m __round__
...
======================================================================
FAIL: __round__ (decimal.Decimal)
Doctest: decimal.Decimal.__round__
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/doctest.py", line 2250, in runTest
    raise self.failureException(self.format_failure(new.getvalue()))
AssertionError: Failed doctest test for decimal.Decimal.__round__
  File "/home/serhiy/py/cpython/Lib/decimal.py", line unknown line number, in __round__

----------------------------------------------------------------------
File "/home/serhiy/py/cpython/Lib/decimal.py", line ?, in decimal.Decimal.__round__
Failed example:
    round(Decimal('-Infinity'), 37)
Exception raised:
    Traceback (most recent call last):
      File "/home/serhiy/py/cpython/Lib/doctest.py", line 1374, in __run
        exec(compile(example.source, filename, "single",
      File "<doctest decimal.Decimal.__round__[10]>", line 1, in <module>
        round(Decimal('-Infinity'), 37)
      File "/home/serhiy/py/cpython/Lib/_pydecimal.py", line 1892, in __round__
        return self.quantize(exp)
               ^^^^^^^^^^^^^^^^^^
      File "/home/serhiy/py/cpython/Lib/_pydecimal.py", line 2566, in quantize
        return context._raise_error(InvalidOperation,
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/serhiy/py/cpython/Lib/_pydecimal.py", line 4058, in _raise_error
        raise error(explanation)
    decimal.InvalidOperation: quantize with one INF
----------------------------------------------------------------------
File "/home/serhiy/py/cpython/Lib/decimal.py", line ?, in decimal.Decimal.__round__
Failed example:
    round(Decimal('sNaN123'), 0)
Exception raised:
    Traceback (most recent call last):
      File "/home/serhiy/py/cpython/Lib/doctest.py", line 1374, in __run
        exec(compile(example.source, filename, "single",
      File "<doctest decimal.Decimal.__round__[11]>", line 1, in <module>
        round(Decimal('sNaN123'), 0)
      File "/home/serhiy/py/cpython/Lib/_pydecimal.py", line 1892, in __round__
        return self.quantize(exp)
               ^^^^^^^^^^^^^^^^^^
      File "/home/serhiy/py/cpython/Lib/_pydecimal.py", line 2559, in quantize
        ans = self._check_nans(exp, context)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/serhiy/py/cpython/Lib/_pydecimal.py", line 776, in _check_nans
        return context._raise_error(InvalidOperation, 'sNaN',
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/home/serhiy/py/cpython/Lib/_pydecimal.py", line 4058, in _raise_error
        raise error(explanation)
    decimal.InvalidOperation: sNaN


----------------------------------------------------------------------

CPython versions tested on:

3.11, 3.12, CPython main branch

Operating systems tested on:

No response

Linked PRs

• gh-109861: Fix a doctest in Lib/_pydecimal.py which was failing when running its doctests directly. #125479
• [3.15] gh-109861: Fix a doctest in Lib/_pydecimal.py which was failing when running its doctests directly (GH-125479) #155287
• [3.14] gh-109861: Fix a doctest in Lib/_pydecimal.py which was failing when running its doctests directly (GH-125479) #155288
• [3.13] gh-109861: Fix a doctest in Lib/_pydecimal.py which was failing when running its doctests directly (GH-125479) #155289

[serhiy-storchaka]

cc @mdickinson

[skirpichev]

Fixed by 2d7ff6e

[mbyrnepr2]

The fix appears to work perfectly when using ./python.exe -m test -v test_decimal -m __round__ but
I see a couple of failing doctests when running it directly with the following commands:

./python.exe -m doctest Lib/decimal.py

markbyrne@Marks-Air-2 cpython % ./python.exe -m doctest Lib/decimal.py
**********************************************************************
File "/Users/markbyrne/programming/cpython/Lib/decimal.py", line 66, in decimal
Failed example:
    print(dig / 0)
Expected:
    Traceback (most recent call last):
      ...
      ...
      ...
    decimal.DivisionByZero: x / 0
Got:
    Traceback (most recent call last):
      File "/Users/markbyrne/programming/cpython/Lib/doctest.py", line 1395, in __run
        exec(compile(example.source, filename, "single",
        ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     compileflags, True), test.globs)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "<doctest decimal[24]>", line 1, in <module>
        print(dig / 0)
              ~~~~^~~
    decimal.DivisionByZero: [<class 'decimal.DivisionByZero'>]
**********************************************************************
File "/Users/markbyrne/programming/cpython/Lib/decimal.py", line 84, in decimal
Failed example:
    print(c.divide(Decimal(0), Decimal(0)))
Expected:
    Traceback (most recent call last):
      ...
      ...
      ...
    decimal.InvalidOperation: 0 / 0
Got:
    Traceback (most recent call last):
      File "/Users/markbyrne/programming/cpython/Lib/doctest.py", line 1395, in __run
        exec(compile(example.source, filename, "single",
        ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     compileflags, True), test.globs)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "<doctest decimal[33]>", line 1, in <module>
        print(c.divide(Decimal(0), Decimal(0)))
              ~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
    decimal.InvalidOperation: [<class 'decimal.DivisionUndefined'>]
**********************************************************************
1 item had failures:
   2 of  39 in decimal
***Test Failed*** 2 failures.

./python.exe -m doctest Lib/_pydecimal.py

markbyrne@Marks-Air-2 cpython % ./python.exe -m doctest Lib/_pydecimal.py
**********************************************************************
File "/Users/markbyrne/programming/cpython/Lib/_pydecimal.py", line 1799, in decimal.Decimal.__round__
Failed example:
    round(Decimal('-Infinity'), 37)
Exception raised:
    Traceback (most recent call last):
      File "/Users/markbyrne/programming/cpython/Lib/doctest.py", line 1395, in __run
        exec(compile(example.source, filename, "single",
        ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     compileflags, True), test.globs)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "<doctest decimal.Decimal.__round__[10]>", line 1, in <module>
        round(Decimal('-Infinity'), 37)
        ~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/markbyrne/programming/cpython/Lib/_pydecimal.py", line 1810, in __round__
        return self.quantize(exp)
               ~~~~~~~~~~~~~^^^^^
      File "/Users/markbyrne/programming/cpython/Lib/_pydecimal.py", line 2495, in quantize
        return context._raise_error(InvalidOperation,
               ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
                                'quantize with one INF')
                                ^^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/markbyrne/programming/cpython/Lib/_pydecimal.py", line 3987, in _raise_error
        raise error(explanation)
    decimal.InvalidOperation: quantize with one INF
**********************************************************************
File "/Users/markbyrne/programming/cpython/Lib/_pydecimal.py", line 1801, in decimal.Decimal.__round__
Failed example:
    round(Decimal('sNaN123'), 0)
Exception raised:
    Traceback (most recent call last):
      File "/Users/markbyrne/programming/cpython/Lib/doctest.py", line 1395, in __run
        exec(compile(example.source, filename, "single",
        ~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                     compileflags, True), test.globs)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      File "<doctest decimal.Decimal.__round__[11]>", line 1, in <module>
        round(Decimal('sNaN123'), 0)
        ~~~~~^^^^^^^^^^^^^^^^^^^^^^^
      File "/Users/markbyrne/programming/cpython/Lib/_pydecimal.py", line 1810, in __round__
        return self.quantize(exp)
               ~~~~~~~~~~~~~^^^^^
      File "/Users/markbyrne/programming/cpython/Lib/_pydecimal.py", line 2488, in quantize
        ans = self._check_nans(exp, context)
      File "/Users/markbyrne/programming/cpython/Lib/_pydecimal.py", line 694, in _check_nans
        return context._raise_error(InvalidOperation, 'sNaN',
               ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^
                                self)
                                ^^^^^
      File "/Users/markbyrne/programming/cpython/Lib/_pydecimal.py", line 3987, in _raise_error
        raise error(explanation)
    decimal.InvalidOperation: sNaN
**********************************************************************
1 item had failures:
   2 of  12 in decimal.Decimal.__round__
***Test Failed*** 2 failures.

Patch which makes the above two commands succeed

markbyrne@Marks-Air-2 cpython % git diff
diff --git a/Lib/_pydecimal.py b/Lib/_pydecimal.py
index 5b60570c6c5..81bb04363f9 100644
--- a/Lib/_pydecimal.py
+++ b/Lib/_pydecimal.py
@@ -1796,9 +1796,10 @@ def __round__(self, n=None):
         Decimal('123.46')
         >>> round(Decimal('123.456'), -2)
         Decimal('1E+2')
-        >>> round(Decimal('-Infinity'), 37)
+        >>> with localcontext(ExtendedContext):
+        ...     round(Decimal('-Infinity'), 37)
+        ...     round(Decimal('sNaN123'), 0)
         Decimal('NaN')
-        >>> round(Decimal('sNaN123'), 0)
         Decimal('NaN123')
 
         """
diff --git a/Lib/decimal.py b/Lib/decimal.py
index 530bdfb3895..5fde9b1584f 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -68,7 +68,7 @@
   ...
   ...
   ...
-decimal.DivisionByZero: x / 0
+decimal.DivisionByZero: [<class 'decimal.DivisionByZero'>]
 >>> c = Context()
 >>> c.traps[InvalidOperation] = 0
 >>> print(c.flags[InvalidOperation])
@@ -86,7 +86,7 @@
   ...
   ...
   ...
-decimal.InvalidOperation: 0 / 0
+decimal.InvalidOperation: [<class 'decimal.DivisionUndefined'>]

Do you think it deserves a separate issue?

[skirpichev]

Do you think it deserves a separate issue?

Probably, no.

./python.exe -m doctest Lib/decimal.py

In this case you should override default options to IGNORE_EXCEPTION_DETAIL.

./python.exe -m doctest Lib/_pydecimal.py

Works for me with

diff --git a/Lib/_pydecimal.py b/Lib/_pydecimal.py
index 75df3db262..241ec4e118 100644
--- a/Lib/_pydecimal.py
+++ b/Lib/_pydecimal.py
@@ -1749,6 +1749,7 @@ def __round__(self, n=None):
         and lies exactly halfway between two integers then it is
         rounded to the integer with even last digit.
 
+        >>> setcontext(ExtendedContext)
         >>> round(Decimal('123.456'))
         123
         >>> round(Decimal('-456.789'))