diff --git a/CMakeLists.txt b/CMakeLists.txt
index c4c8b3e..d07a05d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,10 +7,7 @@ INCLUDE(version)
 
 SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
 
-FIND_PACKAGE(PythonInterp 2 REQUIRED)
-IF (NOT PYTHON_VERSION_MAJOR EQUAL 2)
-  MESSAGE(FATAL_ERROR "Python 2 is required.")
-ENDIF()
+FIND_PACKAGE(PythonInterp 2)
 
 FIND_PROGRAM(CTYPESGEN_FOUND ctypesgen.py)
 
diff --git a/ast/ast.py b/ast/ast.py
index dbe539c..99ce1d9 100644
--- a/ast/ast.py
+++ b/ast/ast.py
@@ -54,6 +54,13 @@ def print_ast(lang_module, input_file):
 if __name__ == '__main__':
   import sys
   lang = sys.argv[1]
+
+  try:
+      if sys.version_info >= (3,0):
+        lang = "%s_py3" % lang
+  except:
+      pass
+
   filename = sys.argv[2]
 
   lang_module = load_lang(lang)
diff --git a/ast/c_impl_py3.py b/ast/c_impl_py3.py
new file mode 100644
index 0000000..aa17765
--- /dev/null
+++ b/ast/c_impl_py3.py
@@ -0,0 +1,61 @@
+# Copyright (c) 2015-present, Facebook, Inc.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from c_py3 import field_prototype, return_type, struct_name
+from casing import title
+from license import C_LICENSE_COMMENT
+
+class Printer(object):
+  '''Printer for the implementation of the pure C interface to the AST.
+  '''
+
+  def __init__(self):
+    self._current_type = None
+
+  def start_file(self):
+    print(C_LICENSE_COMMENT + '''/** @generated */
+
+#include "GraphQLAst.h"
+#include "../Ast.h"
+
+using namespace facebook::graphql::ast;  // NOLINT
+''')
+
+  def end_file(self):
+    pass
+
+  def start_type(self, name):
+    self._current_type = name
+
+  def field(self, type, name, nullable, plural):
+    print(field_prototype(self._current_type, type, name, nullable, plural) + ' {')
+    print('  const auto *realNode = reinterpret_cast<const %s *>(node);' % self._current_type)
+    title_name = title(name)
+    call_get = 'realNode->get%s()' % title_name
+    if plural:
+      if nullable:
+        print('  return %s ? %s->size() : 0;' % (call_get, call_get))
+      else:
+        print('  return %s.size();' % call_get)
+    else:
+      if type in ['string', 'OperationKind', 'boolean']:
+        print('  return %s;' % call_get)
+      else:
+        fmt = '  return reinterpret_cast<const struct %s *>(%s%s);'
+        print(fmt % (struct_name(type), '' if nullable else '&', call_get))
+
+    print('}')
+
+  def end_type(self, name):
+    pass
+
+  def start_union(self, name):
+    pass
+
+  def union_option(self, option):
+    pass
+
+  def end_union(self, name):
+    pass
diff --git a/ast/c_py3.py b/ast/c_py3.py
new file mode 100644
index 0000000..bbcb653
--- /dev/null
+++ b/ast/c_py3.py
@@ -0,0 +1,100 @@
+# Copyright (c) 2015-present, Facebook, Inc.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from casing import snake
+
+from license import C_LICENSE_COMMENT
+
+def struct_name(type):
+  return 'GraphQLAst' + type
+
+
+def return_type(type):
+  if type == 'OperationKind' or type == 'string':
+    return 'const char *'
+
+  if type == 'boolean':
+    return 'int'
+
+  return 'const struct %s *' % struct_name(type)
+
+
+def field_prototype(owning_type, type, name, nullable, plural):
+  st_name = struct_name(owning_type)
+  if plural:
+    return 'int %s_get_%s_size(const struct %s *node)' % (
+      st_name, snake(name), st_name)
+  else:
+    ret_type = return_type(type)
+    return '%s %s_get_%s(const struct %s *node)' % (
+      ret_type, st_name, snake(name), st_name)
+
+
+class Printer(object):
+  '''Printer for the pure C interface to the AST.
+
+  Merely a set of wrappers around the C++ interface; makes it possible
+  to use the AST from C code and simplifies the task of writing
+  bindings for other langugages.
+
+  The mapping is as follows:
+
+  - For each concrete type, you get an opaque C struct type,
+  accessible only by pointer.
+
+  - For each singular field of a concrete type, you get an accessor
+  function, returning said field in the obvious way.
+
+  - For each plural field of a concrete type, you get an accessor
+  function telling you its size. For access to elements of a plural
+  field, you can use the visitor API.
+
+  - For each union type, you get nothing specific (REVIEW), but you
+    can use the visitor API to work around this entirely.
+
+  '''
+
+  def __init__(self):
+    self._current_type = None
+
+  def start_file(self):
+    print(C_LICENSE_COMMENT + '''/** @generated */
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+''')
+
+  def end_file(self):
+    print('''
+
+#ifdef __cplusplus
+}
+#endif
+''')
+
+  def start_type(self, name):
+    # Forward declarations for AST nodes.
+    st_name = struct_name(name)
+    print('struct ' + st_name + ';')
+    self._current_type = name
+
+  def field(self, type, name, nullable, plural):
+    print(field_prototype(self._current_type, type, name, nullable, plural) + ';')
+
+  def end_type(self, name):
+    print()
+
+  def start_union(self, name):
+    print('struct ' + struct_name(name) + ';')
+
+  def union_option(self, option):
+    pass
+
+  def end_union(self, name):
+    print()
diff --git a/ast/c_visitor_impl_py3.py b/ast/c_visitor_impl_py3.py
new file mode 100644
index 0000000..bbf84f0
--- /dev/null
+++ b/ast/c_visitor_impl_py3.py
@@ -0,0 +1,39 @@
+# Copyright (c) 2015-present, Facebook, Inc.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from casing import snake
+from license import C_LICENSE_COMMENT
+
+class Printer(object):
+  '''Printer for a simple list of types to be visited by the C visitor.
+  '''
+
+  def __init__(self):
+    self._types = []
+
+  def start_file(self):
+    print(C_LICENSE_COMMENT + '/** @generated */')
+    print('#define FOR_EACH_CONCRETE_TYPE(MACRO) \\')
+
+  def start_type(self, name):
+    self._types.append(name)
+
+  def field(self, type, name, nullable, plural):
+    pass
+
+  def end_type(self, name):
+    pass
+
+  def end_file(self):
+    print(' \\\n'.join('MACRO(%s, %s)' % (name, snake(name)) for name in self._types))
+
+  def start_union(self, name):
+    pass
+
+  def union_option(self, option):
+    pass
+
+  def end_union(self, name):
+    pass
diff --git a/ast/cxx_impl_py3.py b/ast/cxx_impl_py3.py
new file mode 100644
index 0000000..299ed74
--- /dev/null
+++ b/ast/cxx_impl_py3.py
@@ -0,0 +1,61 @@
+# Copyright (c) 2015-present, Facebook, Inc.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from license import C_LICENSE_COMMENT
+
+class Printer(object):
+  def __init__(self):
+    pass
+
+  def start_file(self):
+    print(C_LICENSE_COMMENT + '''/** @generated */
+
+#include "Ast.h"
+#include "AstVisitor.h"
+
+namespace facebook {
+namespace graphql {
+namespace ast {
+''')
+
+  def end_file(self):
+    print('}  // namespace ast')
+    print('}  // namespace graphql')
+    print('}  // namespace facebook')
+
+  def start_type(self, name):
+    print('''void %s::accept(visitor::AstVisitor *visitor) const {
+  if (visitor->visit%s(*this)) {
+''' % (name, name))
+
+  def field(self, type, name, nullable, plural):
+    if type in ['OperationKind', 'string', 'boolean']:
+      return
+  
+    if plural:
+      accept = '{ for (const auto &x : *%s_) { x->accept(visitor); } }' % name
+      if nullable:
+        accept = 'if (%s_) %s' % (name, accept)
+      print('    ' + accept)
+    else:
+      accept = '%s_->accept(visitor);' % name
+      if nullable:
+        accept = 'if (%s_) { %s }' % (name, accept)
+      print('    ' + accept)
+
+  def end_type(self, name):
+    print('''  }
+  visitor->endVisit%s(*this);
+}
+''' % name)
+
+  def start_union(self, name):
+    pass
+
+  def union_option(self, option):
+    pass
+
+  def end_union(self, name):
+    pass
diff --git a/ast/cxx_json_visitor_header_py3.py b/ast/cxx_json_visitor_header_py3.py
new file mode 100644
index 0000000..8ce7349
--- /dev/null
+++ b/ast/cxx_json_visitor_header_py3.py
@@ -0,0 +1,42 @@
+# Copyright (c) 2016-present, Facebook, Inc.
+# All rights reserved.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from casing import title
+from license import C_LICENSE_COMMENT
+
+class Printer(object):
+  def __init__(self):
+    self._anyFieldIsANode = False
+
+  def start_file(self):
+    print(C_LICENSE_COMMENT + '/** @generated */')
+
+  def end_file(self):
+    pass
+
+  def start_type(self, name):
+    self._anyFieldIsANode = False
+
+  def end_type(self, name):
+    titleName = title(name)
+    if self._anyFieldIsANode:
+      print('bool visit%s(const %s &node) override;' % (titleName, titleName))
+    print('void endVisit%s(const %s &node) override;' % (titleName, titleName))
+    print()
+
+  def field(self, type, name, nullable, plural):
+    if (not self._anyFieldIsANode and
+        type not in ('OperationKind', 'string', 'boolean')):
+      self._anyFieldIsANode = True
+
+  def start_union(self, name):
+    pass
+
+  def union_option(self, option):
+    pass
+
+  def end_union(self, name):
+    pass
diff --git a/ast/cxx_json_visitor_impl_py3.py b/ast/cxx_json_visitor_impl_py3.py
new file mode 100644
index 0000000..c96efdf
--- /dev/null
+++ b/ast/cxx_json_visitor_impl_py3.py
@@ -0,0 +1,80 @@
+# Copyright (c) 2016-present, Facebook, Inc.
+# All rights reserved.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from casing import title
+from license import C_LICENSE_COMMENT
+
+class Printer(object):
+  def __init__(self):
+    self._fields = []
+
+  def start_file(self):
+    print(C_LICENSE_COMMENT + '/** @generated */')
+
+  def end_file(self):
+    pass
+
+  def start_type(self, name):
+    self._fields = []
+
+  def field(self, type, name, nullable, plural):
+    if type == 'OperationKind':
+      type = 'string'
+    self._fields.append((type, name, nullable, plural))
+
+  def end_type(self, name):
+    titleName = title(name)
+    anyFieldIsANode = any(type not in ('string, boolean')
+                          for (type, _, _ ,_) in self._fields)
+    if anyFieldIsANode:
+      print('''bool JsonVisitor::visit%s(const %s &node) {
+  visitNode();
+  return true;
+}
+''' % (titleName, titleName))
+    print('''void JsonVisitor::endVisit%(tn)s(const %(tn)s &node) {
+  NodeFieldPrinter fields(*this, "%(tn)s", node);''' % {'tn': titleName})
+
+    for (type, fieldName, nullable, plural) in self._fields:
+      funcName = None
+      if type == 'string':
+        assert not plural, 'plural string fields not supported yet'
+        funcName = 'printSingularPrimitiveField'
+      elif type == 'boolean':
+        assert not plural, 'plural boolean fields not supported yet'
+        funcName = 'printSingularBooleanField'
+      elif not nullable and not plural:
+        # Special case: singular object fields don't need the value passed.
+        print('  fields.printSingularObjectField("%s");' % fieldName)
+        continue
+      else:
+        nullable_str = 'Nullable' if nullable else ''
+        plural_str = 'Plural' if plural else 'SingularObject'
+        funcName = 'print%s%sField' % (nullable_str, plural_str)
+
+      assert funcName is not None
+      print('  fields.%s("%s", node.get%s());' % (
+        funcName, fieldName, title(fieldName)))
+
+    if anyFieldIsANode:
+      print('''
+  endVisitNode(fields.finishPrinting());
+}
+''')
+    else:
+      print('''
+  printed_.back().emplace_back(fields.finishPrinting());
+}
+''')
+
+  def start_union(self, name):
+    pass
+
+  def union_option(self, option):
+    pass
+
+  def end_union(self, name):
+    pass
diff --git a/ast/cxx_py3.py b/ast/cxx_py3.py
new file mode 100644
index 0000000..cd868be
--- /dev/null
+++ b/ast/cxx_py3.py
@@ -0,0 +1,197 @@
+# Copyright (c) 2015-present, Facebook, Inc.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+import io as StringIO
+
+from casing import title
+from license import C_LICENSE_COMMENT
+
+class Printer(object):
+  def __init__(self):
+    self._type_name = None
+    # Map concrete type to base class
+    self._bases = {}
+    # HACK: Defer everything we print so that forward declarations for
+    # all classes come first. Avoids having to do 2 passes over the
+    # input file.
+    self._deferredOutput = StringIO.StringIO()
+
+    self._fields = []
+
+  def start_file(self):
+    print(C_LICENSE_COMMENT + '''/** @generated */
+#pragma once
+
+#include "AstNode.h"
+
+#include <memory>
+#include <string>
+#include <utility>
+#include <vector>
+
+namespace facebook {
+namespace graphql {
+namespace ast {
+
+// The parser uses strdup to move from yytext to the heap, so we need
+// to use free instead of delete.
+struct CDeleter {
+  void operator()(const char *p) const { free((void *)p); }
+};
+''')
+
+  def end_file(self):
+    print()
+    print(self._deferredOutput.getvalue())
+    print('}')
+    print('}')
+    print('}')
+
+  def _base_class(self, type):
+    return self._bases.get(type, 'Node')
+
+  def start_type(self, name):
+    self._type_name = name
+    base = self._base_class(name)
+    # non-deferred!
+    print('class %s;' % name)
+    print('class %s : public %s {' % (name, base), file=self._deferredOutput)
+    self._fields = []
+
+  def field(self, type, name, nullable, plural):
+    if type == 'OperationKind':
+      type = 'string'
+    self._fields.append((type, name, nullable, plural))
+
+  def end_type(self, name):
+    self._print_fields()
+    print(' public:', file=self._deferredOutput)
+    self._print_constructor()
+    print(file=self._deferredOutput)
+    self._print_destructor_prototype()
+    print(file=self._deferredOutput)
+    self._print_noncopyable()
+    print(file=self._deferredOutput)
+    self._print_getters()
+    print('  void accept(visitor::AstVisitor *visitor) const override;', file=self._deferredOutput)
+    print('};', file=self._deferredOutput)
+    print(file=self._deferredOutput)
+    print(file=self._deferredOutput)
+    self._type_name = None
+    self._fields = []
+
+  def _storage_type(self, type):
+    if type == 'string':
+      return 'std::unique_ptr<const char, CDeleter>'
+    elif type == 'boolean':
+      return 'bool'
+    else:
+      return 'std::unique_ptr<%s>' % type
+
+  def _print_fields(self):
+    for (type, name, nullable, plural) in self._fields:
+      storage_type = self._storage_type(type)
+      if plural:
+        storage_type = 'std::unique_ptr<std::vector<%s>>' % storage_type
+      print('  %s %s_;' % (storage_type, name), file=self._deferredOutput)
+
+  def _ctor_singular_type(self, type):
+    if type == 'string':
+      return 'const char *'
+    elif type == 'boolean':
+      return 'bool'
+    else:
+      return '%s *' % type
+
+  def _ctor_plural_type(self, type):
+    return 'std::vector<%s> *' % self._storage_type(type)
+
+  def _print_constructor(self):
+    print('  explicit %s(' % self._type_name, file=self._deferredOutput)
+    print('      const yy::location &location%s' % (',' if self._fields else ''), file=self._deferredOutput)
+    def ctor_arg(type, name, plural):
+      if plural:
+        ctor_type = self._ctor_plural_type(type)
+      else:
+        ctor_type = self._ctor_singular_type(type)
+      return '      %s %s' % (ctor_type, name)
+    print(',\n'.join(ctor_arg(type, name, plural)
+                     for (type, name, nullable, plural) in self._fields), file=self._deferredOutput)
+    print('  )', file=self._deferredOutput)
+    def ctor_init(type, name, plural):
+      # Strings are const char *, just pass.
+      # Vectors are passed by pointer and we take ownership.
+      # Node types are passed in by pointer and we take ownership.
+      value = name
+      return '    %s_(%s)' % (name, value)
+    print('  : %s(location)%s' % (self._base_class(self._type_name), ',' if self._fields else ''), file=self._deferredOutput)
+    print(',\n'.join(ctor_init(type, name, plural)
+                     for (type, name, nullable, plural)
+                     in self._fields), file=self._deferredOutput)
+    print('  {}', file=self._deferredOutput)
+
+  def _getter_type(self, type, nullable, plural):
+    if plural and nullable:
+      return 'const std::vector<%s>*' % self._storage_type(type)
+    elif plural:
+      return 'const std::vector<%s>&' %  self._storage_type(type)
+
+    if type == 'string':
+      assert not nullable
+      return 'const char *'
+    elif type == 'boolean':
+      assert not nullable
+      return 'bool'
+    elif nullable:
+      return 'const %s*' % type
+    else:
+      return 'const %s&' % type
+
+  def _getter_value_to_return(self, raw_value, type, nullable, plural):
+    if plural and nullable:
+      return raw_value + '.get()'
+    elif plural:
+      return '*%s' % raw_value
+    elif type == 'boolean':
+      return raw_value
+    elif nullable or type == 'string':
+      return '%s.get()' % raw_value
+    else:
+      return '*%s' % raw_value
+
+  def _print_getters(self):
+    for (type, name, nullable, plural) in self._fields:
+      print('  %s get%s() const' % (
+        self._getter_type(type, nullable, plural),
+        title(name)), file=self._deferredOutput)
+      print('  { return %s; }' % (
+        self._getter_value_to_return(name + '_', type, nullable, plural)), file=self._deferredOutput)
+      print(file=self._deferredOutput)
+
+  def _print_destructor_prototype(self):
+    print('  ~%s() {}' % self._type_name, file=self._deferredOutput)
+
+  def _print_noncopyable(self):
+    print('  %s(const %s&) = delete;' % (
+      self._type_name, self._type_name), file=self._deferredOutput)
+    print('  %s& operator=(const %s&) = delete;' % (
+      self._type_name, self._type_name), file=self._deferredOutput)
+  
+  def start_union(self, name):
+    self._type_name = name
+    # non-deferred!
+    print('class %s;' % name)
+    print('class %s : public Node {' % name, file=self._deferredOutput)
+    print(' public:', file=self._deferredOutput)
+    self._print_constructor()
+    print('};', file=self._deferredOutput)
+    print(file=self._deferredOutput)
+
+  def union_option(self, type):
+    assert type not in self._bases, '%s cannot appear in more than one union!' % type
+    self._bases[type] = self._type_name
+
+  def end_union(self, name):
+    pass
diff --git a/ast/cxx_visitor_py3.py b/ast/cxx_visitor_py3.py
new file mode 100644
index 0000000..ac15cae
--- /dev/null
+++ b/ast/cxx_visitor_py3.py
@@ -0,0 +1,64 @@
+# Copyright (c) 2015-present, Facebook, Inc.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+from casing import camel, title
+from license import C_LICENSE_COMMENT
+
+class Printer(object):
+  def __init__(self):
+    pass
+
+  def start_file(self):
+    print(C_LICENSE_COMMENT + '''/** @generated */
+
+#pragma once
+
+#include "Ast.h"
+
+namespace facebook {
+namespace graphql {
+namespace ast {
+namespace visitor {
+
+class AstVisitor {
+public:
+  virtual ~AstVisitor() {}
+''')
+
+  def end_file(self):
+    print('};') # end AstVisitor
+    print()
+    print('}')
+    print('}')
+    print('}')
+    print('}')
+
+  def start_type(self, name):
+    titleName = title(name)
+    camelName = camel(titleName)
+    print('  virtual bool visit%s(const %s &%s) { return true; }' % (
+      titleName,
+      titleName,
+      camelName))
+    print('  virtual void endVisit%s(const %s &%s) { }' % (
+      titleName,
+      titleName,
+      camelName))
+    print()
+
+  def end_type(self, name):
+    pass
+
+  def field(self, type, name, nullable, plural):
+    pass
+
+  def start_union(self, name):
+    pass
+
+  def union_option(self, option):
+    pass
+
+  def end_union(self, name):
+    pass
diff --git a/ast/js_py3.py b/ast/js_py3.py
new file mode 100644
index 0000000..68aee6e
--- /dev/null
+++ b/ast/js_py3.py
@@ -0,0 +1,65 @@
+# Copyright (c) 2015-present, Facebook, Inc.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+
+class Printer(object):
+  def __init__(self):
+    pass
+
+  def start_file(self):
+    print('''/* @flow */
+/* @generated */
+/* jshint ignore:start */
+
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+type Node = {
+  kind: string;
+  start?: ?number;
+  end?: ?number;
+};
+
+type OperationKind = 'query' | 'mutation' | 'subscription';''')
+
+  def end_file(self):
+    pass
+
+  def start_type(self, name):
+    print()
+    print('type %s = Node & {' % name)
+    kind = name
+    if kind == 'GenericType':
+      kind = 'Type'
+    print('  kind: \'%s\';' % kind)
+
+  def end_type(self, name):
+    print('}')
+
+  def _js_type(self, type, plural):
+    if plural:
+      type = 'Array<%s>' % type
+    return type
+
+  def field(self, type, name, nullable, plural):
+    nullable_char = '?' if nullable else ''
+    js_type = self._js_type(type, plural)
+    print('  %(name)s%(nullable_char)s: %(nullable_char)s%(js_type)s;' % locals())
+
+  def start_union(self, name):
+    print(('type %s = ' % name), end=' ')
+    self._current_options = []
+
+  def union_option(self, type):
+    self._current_options.append(type)
+
+  def end_union(self, name):
+    print('\n  | '.join(self._current_options))
+    print()
+    self._current_options = None