added 'decoupled' kwparam to merge() (closes #115)

src/configobj/__init__.py

@@ -20,6 +20,7 @@
 import os
 import re
 import sys
+import copy
 import collections
 
 from codecs import BOM_UTF8, BOM_UTF16, BOM_UTF16_BE, BOM_UTF16_LE
@@ -729,10 +730,15 @@ def dict(self):
         return newdict
 
 
-    def merge(self, indict):
+    def merge(self, indict, decoupled=False):
         """
         A recursive update - useful for merging config files.
 
+        Note: if ``decoupled`` is ``True``, then the target object (self)
+        gets its own copy of any mutable objects in the source dictionary
+        (both sections and values), paid for by more work for ``merge()``
+        and more memory usage.
+
         >>> a = '''[section1]
         ...     option1 = True
         ...     [[subsection]]
@@ -749,9 +755,11 @@ def merge(self, indict):
         ConfigObj({'section1': {'option1': 'False', 'subsection': {'more_options': 'False'}}})
         """
         for key, val in list(indict.items()):
+            if decoupled:
+                val = copy.deepcopy(val)
             if (key in self and isinstance(self[key], collections.Mapping) and
                                 isinstance(val, collections.Mapping)):
-                self[key].merge(val)
+                self[key].merge(val, decoupled=decoupled)
             else:
                 self[key] = val
 

src/tests/test_configobj.py

@@ -1251,6 +1251,18 @@ def test_interpolation_using_default_sections():
     assert c.write() == ['a = %(a)s', '[DEFAULT]', 'a = fish']
 
 
+class TestMerging(object):
+
+    @pytest.mark.parametrize('data', ((False, 42), (True, '3')))
+    def test_merge_coupling(self, data):
+        c1 = ConfigObj("foo = 1,2|[sect]|val=3".split('|'))
+        c2 = ConfigObj("bar = 3".split('|'))
+        c2.merge(c1, decoupled=data[0])
+        assert c2['sect']['val'] == '3'
+        c1['sect']['val'] = 42
+        assert c2['sect']['val'] == data[1]
+
+
 class TestErrorReporting(object):
     MULTI_ERROR = [
         '[]',