From 3b24ccbe7e2b43c4373e4b1e988df55978b819e7 Mon Sep 17 00:00:00 2001
From: Mark Dickinson <dickinsm@gmail.com>
Date: Tue, 25 Mar 2008 14:33:23 +0000
Subject: [PATCH] Issue #2478: Decimal(sqrt(0)) failed when the decimal context
 was not explicitly supplied.

---
 Lib/decimal.py           | 6 +++---
 Lib/test/test_decimal.py | 6 ++++++
 Misc/NEWS                | 2 ++
 3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/Lib/decimal.py b/Lib/decimal.py
index 5d25012bd07..b775bee3e3c 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -2453,6 +2453,9 @@ class Decimal(object):
 
     def sqrt(self, context=None):
         """Return the square root of self."""
+        if context is None:
+            context = getcontext()
+
         if self._is_special:
             ans = self._check_nans(context=context)
             if ans:
@@ -2466,9 +2469,6 @@ class Decimal(object):
             ans = _dec_from_triple(self._sign, '0', self._exp // 2)
             return ans._fix(context)
 
-        if context is None:
-            context = getcontext()
-
         if self._sign == 1:
             return context._raise_error(InvalidOperation, 'sqrt(-x), x > 0')
 
diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index 5e533185f8d..46d2dc71216 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -1315,6 +1315,12 @@ class DecimalUsabilityTest(unittest.TestCase):
         d = d1.max(d2)
         self.assertTrue(type(d) is Decimal)
 
+    def test_implicit_context(self):
+        # Check results when context given implicitly.  (Issue 2478)
+        c = getcontext()
+        self.assertEqual(str(Decimal(0).sqrt()),
+                         str(c.sqrt(Decimal(0))))
+
 
 class DecimalPythonAPItests(unittest.TestCase):
 
diff --git a/Misc/NEWS b/Misc/NEWS
index 4afd6cad10b..65815f7ab24 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -72,6 +72,8 @@ Extensions Modules
 Library
 -------
 
+- Issue #2478: fix failure of decimal.Decimal(0).sqrt()
+
 - Issue #2432: give DictReader the dialect and line_num attributes
   advertised in the docs.