Add documentation, write tests

python · JelleZijlstra · Apr 22, 2022 · Apr 1, 2022 · Apr 1, 2022 · Apr 1, 2022
commit 16617094346da726f5e40b613b2c5bf64964de7c
diff --git a/Doc/library/decimal.rst b/Doc/library/decimal.rst
@@ -925,12 +925,13 @@ Each thread has its own current context which is accessed or changed using the
 You can also use the :keyword:`with` statement and the :func:`localcontext`
 function to temporarily change the active context.
 
-.. function:: localcontext(ctx=None)
+.. function:: localcontext(ctx=None, \*\*kwargs)
 
    Return a context manager that will set the current context for the active thread
    to a copy of *ctx* on entry to the with-statement and restore the previous context
    when exiting the with-statement. If no context is specified, a copy of the
-   current context is used.
+   current context is used.  The *kwargs* argument is used to specify the attributes
+   of the context that will be returned.
 
    For example, the following code sets the current decimal precision to 42 places,
    performs a calculation, and then automatically restores the previous context::
@@ -942,10 +943,17 @@ function to temporarily change the active context.
           s = calculate_something()
       s = +s  # Round the final result back to the default precision
 
+
+Raises :exc:`TypeError` if *kwargs* supplies an attribute that :class:`Context` doesn't
+support.
+
+Raises :exc:`ValueError` if *kwargs* supplies an invalid value for an attribute.
+
 New contexts can also be created using the :class:`Context` constructor
 described below. In addition, the module provides three pre-made contexts:
 
 
+
 .. class:: BasicContext
 
    This is a standard context defined by the General Decimal Arithmetic

diff --git a/Lib/_pydecimal.py b/Lib/_pydecimal.py
@@ -503,7 +503,10 @@ def sin(x):
     if ctx is None:
         ctx = getcontext()
     for key, value in kwargs.items():
-        setattr(ctx, key, value)
+        try:
+            setattr(ctx, key, value)
+        except:
+            raise TypeError(f"'{key}' is an invalid keyword argument for this function")
     return _ContextManager(ctx)
 
 

diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
@@ -3602,6 +3602,21 @@ def test_localcontextarg(self):
         self.assertIsNot(new_ctx, set_ctx, 'did not copy the context')
         self.assertIs(set_ctx, enter_ctx, '__enter__ returned wrong context')
 
+    def test_localcontext_kwargs(self):
+        with self.decimal.localcontext(
+            prec=10, rounding=ROUND_HALF_DOWN,
+            Emin=-20, Emax=20, capitals=0,
+            clamp=1
+        ) as ctx:
+            self.assertEqual(ctx.prec, 10)
+            self.assertEqual(ctx.rounding, self.decimal.ROUND_HALF_DOWN)
+            self.assertEqual(ctx.Emin, -20)
+            self.assertEqual(ctx.Emax, 20)
+            self.assertEqual(ctx.capitals, 0)
+            self.assertEqual(ctx.clamp, 1)
+
+        self.assertRaises(TypeError, self.decimal.localcontext, precision=10)
+
     def test_nested_with_statements(self):
         # Use a copy of the supplied context in the block
         Decimal = self.decimal.Decimal

diff --git a/Modules/_decimal/docstrings.h b/Modules/_decimal/docstrings.h
@@ -30,7 +30,7 @@ Set a new default context.\n\
 \n");
 
 PyDoc_STRVAR(doc_localcontext,
-"localcontext($module, /, ctx=None)\n--\n\n\
+"localcontext($module, /, ctx=None, **kwargs)\n--\n\n\
 Return a context manager that will set the default context to a copy of ctx\n\
 on entry to the with-statement and restore the previous default context when\n\
 exiting the with-statement. If no context is specified, a copy of the current\n\