futurize: Prevent any encoding or shebang prefixes to print statements from appearing twice in the output

Author: edschofield

src/libfuturize/fixer_util.py

@@ -200,7 +200,7 @@ def future_import(feature, node):
     shebang_encoding_idx = None
 
     for idx, node in enumerate(root.children):
-        # If it's a shebang or encoding line, attach the prefix to
+        # Is it a shebang or encoding line?
         if is_shebang_comment(node) or is_encoding_comment(node):
             shebang_encoding_idx = idx
         if node.type == syms.simple_stmt and \
@@ -218,11 +218,13 @@ def future_import(feature, node):
     import_ = FromImport(u'__future__', [Leaf(token.NAME, feature, prefix=" ")])
     if shebang_encoding_idx == 0 and idx == 0:
         # If this __future__ import would go on the first line,
-        # detach the shebang / encoding prefix from the current first line
+        # detach the shebang / encoding prefix from the current first line.
         # and attach it to our new __future__ import node.
-        import_.prefix = root.children[0].prefix
-        root.children[0].prefix = u''
-    children = [import_, Newline()]
+        import_.set_prefix(root.children[0].get_prefix())
+        root.children[0].set_prefix(u'')
+        # End the __future__ import line with a newline and add a blank line
+        # afterwards:
+    children = [import_ , Newline()]
     root.insert_child(idx, Node(syms.simple_stmt, children))
 
 

src/libfuturize/fixes/fix_print_with_import.py

@@ -14,7 +14,10 @@
 class FixPrintWithImport(FixPrint):
     run_order = 7
     def transform(self, node, results):
-        n_stmt = super(FixPrintWithImport, self).transform(node, results)
+        # Add the __future__ import first. (Otherwise any shebang or encoding
+        # comment line attached as a prefix to the print statement will be
+        # copied twice and appear twice.)
         future_import(u'print_function', node)
+        n_stmt = super(FixPrintWithImport, self).transform(node, results)
         return n_stmt