Replace enclose decorator with Delimit context manager

Manually cherry-picked from pretty-print branch to introduce in logical order.

astor/code_gen.py

@@ -48,14 +48,23 @@ def to_source(node, indent_with=' ' * 4, add_line_information=False):
     return ''.join(str(s) for s in generator.result)
 
 
-def enclose(enclosure):
-    def decorator(func):
-        def newfunc(self, node):
-            self.write(enclosure[0])
-            func(self, node)
-            self.write(enclosure[-1])
-        return newfunc
-    return decorator
+class Delimit(object):
+    """A context manager that can add enclosing
+       delimiters around the output of a
+       SourceGenerator method.
+    """
+
+    def __init__(self, tree, delimiters='()'):
+        opening, closing = delimiters
+        tree.write(opening)
+        self.closing = delimiters[1]
+        self.result = tree.result
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *exc_info):
+        self.result.append(self.closing)
 
 
 class SourceGenerator(ExplicitNodeVisitor):
@@ -74,6 +83,9 @@ class SourceGenerator(ExplicitNodeVisitor):
         self.indentation = 0
         self.new_lines = 0
 
+    def delimit(self, *args):
+        return Delimit(self, *args)
+
     def write(self, *params):
         for item in params:
             if isinstance(item, ast.AST):
@@ -402,43 +414,43 @@ class SourceGenerator(ExplicitNodeVisitor):
             s = '(%s)' % s
         self.write(s)
 
-    @enclose('()')
     def visit_Tuple(self, node):
+        with self.delimit():
             self.comma_list(node.elts, len(node.elts) == 1)
 
-    @enclose('[]')
     def visit_List(self, node):
+        with self.delimit('[]'):
             self.comma_list(node.elts)
 
-    @enclose('{}')
     def visit_Set(self, node):
+        with self.delimit('{}'):
             self.comma_list(node.elts)
 
-    @enclose('{}')
     def visit_Dict(self, node):
+        with self.delimit('{}'):
             for idx, (key, value) in enumerate(zip(node.keys, node.values)):
                 self.write(', ' if idx else '',
                            key if key else '',
                            ': ' if key else '**', value)
 
-    @enclose('()')
     def visit_BinOp(self, node):
+        with self.delimit():
             self.write(node.left, get_op_symbol(node.op, ' %s '), node.right)
 
-    @enclose('()')
     def visit_BoolOp(self, node):
+        with self.delimit():
             op = get_op_symbol(node.op, ' %s ')
             for idx, value in enumerate(node.values):
                 self.write(idx and op or '', value)
 
-    @enclose('()')
     def visit_Compare(self, node):
+        with self.delimit():
             self.visit(node.left)
             for op, right in zip(node.ops, node.comparators):
                 self.write(get_op_symbol(op, ' %s '), right)
 
-    @enclose('()')
     def visit_UnaryOp(self, node):
+        with self.delimit():
             self.write(get_op_symbol(node.op), '(', node.operand, ')')
 
     def visit_Subscript(self, node):
@@ -460,23 +472,21 @@ class SourceGenerator(ExplicitNodeVisitor):
     def visit_ExtSlice(self, node):
         self.comma_list(node.dims, len(node.dims) == 1)
 
-    @enclose('()')
-    def visit_Yield(self, node):
-        self.write('yield')
+    def visit_Yield(self, node, suffix=''):
+        with self.delimit():
+            self.write('yield%s' % suffix)
             self.conditional_write(' ', node.value)
 
     # new for Python 3.3
-    @enclose('()')
     def visit_YieldFrom(self, node):
-        self.write('yield from')
-        self.conditional_write(' ', node.value)
+        self.visit_Yield(node, ' from')
 
     # new for Python 3.5
     def visit_Await(self, node):
         self.write('await ', node.value)
 
-    @enclose('()')
     def visit_Lambda(self, node):
+        with self.delimit():
             self.write('lambda ')
             self.visit_arguments(node.args)
             self.write(': ', node.body)
@@ -484,32 +494,32 @@ class SourceGenerator(ExplicitNodeVisitor):
     def visit_Ellipsis(self, node):
         self.write('...')
 
-    @enclose('[]')
     def visit_ListComp(self, node):
+        with self.delimit('[]'):
             self.write(node.elt, *node.generators)
 
-    @enclose('()')
     def visit_GeneratorExp(self, node):
+        with self.delimit():
             self.write(node.elt, *node.generators)
 
-    @enclose('{}')
     def visit_SetComp(self, node):
+        with self.delimit('{}'):
             self.write(node.elt, *node.generators)
 
-    @enclose('{}')
     def visit_DictComp(self, node):
+        with self.delimit('{}'):
             self.write(node.key, ': ', node.value, *node.generators)
 
-    @enclose('()')
     def visit_IfExp(self, node):
+        with self.delimit('()'):
             self.write(node.body, ' if ', node.test, ' else ', node.orelse)
 
     def visit_Starred(self, node):
         self.write('*', node.value)
 
-    @enclose('``')
     def visit_Repr(self, node):
         # XXX: python 2.6 only
+        with self.delimit('``'):
             self.visit(node.value)
 
     def visit_Module(self, node):