Fix the wrongheaded implementation of context management in the decimal module and add unit tests. (python-dev discussion is ongoing regarding what we do about Python 2.5)
diff --git a/Lib/decimal.py b/Lib/decimal.py
index 396c413..a5176e6 100644
--- a/Lib/decimal.py
+++ b/Lib/decimal.py
@@ -130,8 +130,11 @@
'ROUND_DOWN', 'ROUND_HALF_UP', 'ROUND_HALF_EVEN', 'ROUND_CEILING',
'ROUND_FLOOR', 'ROUND_UP', 'ROUND_HALF_DOWN',
+ # helper for context management
+ 'ContextManager',
+
# Functions for manipulating contexts
- 'setcontext', 'getcontext'
+ 'setcontext', 'getcontext', 'localcontext'
]
import copy as _copy
@@ -458,6 +461,49 @@
del threading, local # Don't contaminate the namespace
+def localcontext(ctx=None):
+ """Return a context manager for a copy of the supplied context
+
+ Uses a copy of the current context if no context is specified
+ The returned context manager creates a local decimal context
+ in a with statement:
+ def sin(x):
+ with localcontext() as ctx:
+ ctx.prec += 2
+ # Rest of sin calculation algorithm
+ # uses a precision 2 greater than normal
+ return +s # Convert result to normal precision
+
+ def sin(x):
+ with localcontext(ExtendedContext):
+ # Rest of sin calculation algorithm
+ # uses the Extended Context from the
+ # General Decimal Arithmetic Specification
+ return +s # Convert result to normal context
+
+ """
+ # The below can't be included in the docstring until Python 2.6
+ # as the doctest module doesn't understand __future__ statements
+ """
+ >>> from __future__ import with_statement
+ >>> print getcontext().prec
+ 28
+ >>> with localcontext():
+ ... ctx = getcontext()
+ ... ctx.prec() += 2
+ ... print ctx.prec
+ ...
+ 30
+ >>> with localcontext(ExtendedContext):
+ ... print getcontext().prec
+ ...
+ 9
+ >>> print getcontext().prec
+ 28
+ """
+ if ctx is None: ctx = getcontext().copy()
+ return ContextManager(ctx.copy())
+
##### Decimal class ###########################################
@@ -2174,19 +2220,26 @@
del name, val, globalname, rounding_functions
class ContextManager(object):
- """Helper class to simplify Context management.
+ """Context manager class to support localcontext().
+ Sets the supplied context in __enter__() and restores
+ the previous decimal context in __exit__()
+
+ """
+ # The below can't be included in the docstring until Python 2.6
+ # as the doctest module doesn't understand __future__ statements
+ """
Sample usage:
-
- with decimal.ExtendedContext:
- s = ...
- return +s # Convert result to normal precision
-
- with decimal.getcontext() as ctx:
- ctx.prec += 2
- s = ...
- return +s
-
+ >>> from __future__ import with_statement
+ >>> print getcontext().prec
+ 28
+ >>> ctx = Context(prec=15)
+ >>> with ContextManager(ctx):
+ ... print getcontext().prec
+ ...
+ 15
+ >>> print getcontext().prec
+ 28
"""
def __init__(self, new_context):
self.new_context = new_context
@@ -2248,9 +2301,6 @@
s.append('traps=[' + ', '.join([t.__name__ for t, v in self.traps.items() if v]) + ']')
return ', '.join(s) + ')'
- def get_manager(self):
- return ContextManager(self.copy())
-
def clear_flags(self):
"""Reset all flags to zero"""
for flag in self.flags:
diff --git a/Lib/test/test_decimal.py b/Lib/test/test_decimal.py
index f3f9215..6e7faf5 100644
--- a/Lib/test/test_decimal.py
+++ b/Lib/test/test_decimal.py
@@ -23,6 +23,7 @@
you're working through IDLE, you can import this test module and call test_main()
with the corresponding argument.
"""
+from __future__ import with_statement
import unittest
import glob
@@ -1064,6 +1065,43 @@
self.assertNotEqual(id(c.flags), id(d.flags))
self.assertNotEqual(id(c.traps), id(d.traps))
+class WithStatementTest(unittest.TestCase):
+ # Can't do these as docstrings until Python 2.6
+ # as doctest can't handle __future__ statements
+ def test_ContextManager(self):
+ # The basic context manager uses the supplied context
+ # without making a copy of it
+ orig_ctx = getcontext()
+ new_ctx = Context()
+ with ContextManager(new_ctx) as enter_ctx:
+ set_ctx = getcontext()
+ final_ctx = getcontext()
+ self.assert_(orig_ctx is final_ctx, 'did not restore context correctly')
+ self.assert_(new_ctx is set_ctx, 'did not set correct context')
+ self.assert_(set_ctx is enter_ctx, '__enter__ returned wrong context')
+
+ def test_localcontext(self):
+ # The helper function makes a copy of the supplied context
+ orig_ctx = getcontext()
+ with localcontext() as enter_ctx:
+ set_ctx = getcontext()
+ final_ctx = getcontext()
+ self.assert_(orig_ctx is final_ctx, 'did not restore context correctly')
+ self.assert_(orig_ctx is not set_ctx, 'did not copy the context')
+ self.assert_(set_ctx is enter_ctx, '__enter__ returned wrong context')
+
+ def test_localcontextarg(self):
+ # The helper function makes a copy of the supplied context
+ orig_ctx = getcontext()
+ new_ctx = Context(prec=42)
+ with localcontext(new_ctx) as enter_ctx:
+ set_ctx = getcontext()
+ final_ctx = getcontext()
+ self.assert_(orig_ctx is final_ctx, 'did not restore context correctly')
+ self.assert_(set_ctx.prec == new_ctx.prec, 'did not set correct context')
+ self.assert_(new_ctx is not set_ctx, 'did not copy the context')
+ self.assert_(set_ctx is enter_ctx, '__enter__ returned wrong context')
+
def test_main(arith=False, verbose=None):
""" Execute the tests.
@@ -1084,6 +1122,7 @@
DecimalPythonAPItests,
ContextAPItests,
DecimalTest,
+ WithStatementTest,
]
try: