[fix/opti] Fix "Remove redundant deepcopies"

Also, remove more redundant deepcopies

src/zc/buildout/buildout.py

@@ -2275,35 +2275,30 @@ def _dists_sig(dists):
     return result
 
 def _update_section(s1, s2):
-    # Base section 2 on section 1; section 1 is copied, with key-value pairs
-    # 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.
-    # 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])):
+    # Base section 2 on section 1; key-value pairs in s2 override those in s1.
+    # If there are += or -= operators in s2, process these to add or subtract
+    # items (delimited by newlines) from the preexisting values.
+    # Sort on key, then on + and - operators, so that KEY < KEY + < KEY -, to
+    # process them in this order if several are defined in the same section.
+    # Section s1 is modified in place.
+    keysort = lambda x: (x[0].rstrip(' +'), x[0].endswith('+'))
+    for k, v in sorted(s2.items(), key=keysort):
         if k.endswith('+'):
             key = k.rstrip(' +')
-            implicit_value = SectionKey("", "IMPLICIT_VALUE")
-            # Find v1 in s2 first; it may have been defined locally too.
-            section_key = s2.get(key, s1.get(key, implicit_value))
-            section_key = copy.deepcopy(section_key)
-            section_key.addToValue(v.value, v.source)
+            value = s1.get(key, SectionKey("", "IMPLICIT_VALUE"))
+            value.addToValue(v.value, v.source)
+            s1[key] = value
         elif k.endswith('-'):
             key = k.rstrip(' -')
-            implicit_value = SectionKey("", "IMPLICIT_VALUE")
-            # Find v1 in s2 first; it may have been set by a += operation first
-            section_key = s2.get(key, s1.get(key, implicit_value))
-            section_key = copy.deepcopy(section_key)
-            section_key.removeFromValue(v.value, v.source)
+            value = s1.get(key, SectionKey("", "IMPLICIT_VALUE"))
+            value.removeFromValue(v.value, v.source)
+            s1[key] = value
         else:
-            key = k
-            section_key = v
-
-        if key in s1:
-            v1 = s1[key]
-            v1.overrideValue(section_key)
+            if k in s1:
+                v1 = s1[k]
+                v1.overrideValue(v)
             else:
-            s1[key] = section_key
+                s1[k] = v
     return s1
 
 def _update(d1, d2):