[opti] Remove redundant deepcopies

src/zc/buildout/buildout.py

@@ -1986,7 +1986,6 @@ def _update_section(in1, s2):
     # in section 2 overriding those in section 1. If there are += or -=
     # operators in section 2, process these to add or subtract items (delimited
     # by newlines) from the preexisting values.
-    s2 = copy.deepcopy(s2) # avoid mutating the second argument, which is unexpected
     # Sort on key, then on the addition or subtraction operator (+ comes first)
     for k, v in sorted(s2.items(), key=lambda x: (x[0].rstrip(' +'), x[0][-1])):
         if k.endswith('+'):
@@ -1996,8 +1995,6 @@ def _update_section(in1, s2):
             section_key = s2.get(key, s1.get(key, implicit_value))
             section_key = copy.deepcopy(section_key)
             section_key.addToValue(v.value, v.source)
-            s2[key] = section_key
-            del s2[k]
         elif k.endswith('-'):
             key = k.rstrip(' -')
             implicit_value = SectionKey("", "IMPLICIT_VALUE")
@@ -2005,19 +2002,16 @@ def _update_section(in1, s2):
             section_key = s2.get(key, s1.get(key, implicit_value))
             section_key = copy.deepcopy(section_key)
             section_key.removeFromValue(v.value, v.source)
-            s2[key] = section_key
-            del s2[k]
-
-    _update_verbose(s1, s2)
-    return s1
+        else:
+            key = k
+            section_key = v
 
-def _update_verbose(s1, s2):
-    for key, v2 in s2.items():
         if key in s1:
             v1 = s1[key]
-            v1.overrideValue(v2)
+            v1.overrideValue(section_key)
         else:
-            s1[key] = copy.deepcopy(v2)
+            s1[key] = section_key
+    return s1
 
 def _update(in1, d2):
     d1 = copy.deepcopy(in1)