fix_division: always replace with '//' (for now)

my2to3/fixes/fix_division.py

 import builtins
 from collections import defaultdict
 import lib2to3.fixer_base
+import lib2to3.pgen2
+from lib2to3.pygram import python_symbols as syms
+from lib2to3.pytree import Leaf, Node
 import os
 import re
 
@@ -30,6 +33,14 @@ def parse_trace_data(filepath):
   return traces
 
 
+def analyze_data(data):
+  """Indicates whether the division described by `data` should be modified into
+  `//`, or should remain as `/`
+  """
+  # TODO:
+  return True
+
+
 class FixDivision(lib2to3.fixer_base.BaseFix):
   """Rewrites division_traced(n, a, b) into Py2/Py3-compatible division
 
@@ -55,5 +66,21 @@ class FixDivision(lib2to3.fixer_base.BaseFix):
     id_ = int(node.children[1].children[1].children[0].value)
 
     data = self.traces[self.absolute_filename][lineno][id_]
+    if not data:
+      return
 
-    # TODO: analyse `data`, and replace the node to rewrite code
+    if analyze_data(data):
+      operator = Leaf(lib2to3.pgen2.token.DOUBLESLASH, "//")
+    else:
+      operator = Leaf(lib2to3.pgen2.token.SLASH, "/")
+    operator.prefix = node.children[1].children[1].children[3].prefix
+
+    node.replace(
+      Node(
+        syms.term,
+        [
+          node.children[1].children[1].children[2].clone(),
+          operator,
+          node.children[1].children[1].children[4].clone()
+        ],
+        prefix=node.prefix))