diff --git a/CMakeLists.txt b/CMakeLists.txt
index dd55f05..2a909bf 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..1ba028e 100644
--- a/ast/ast.py
+++ b/ast/ast.py
@@ -53,6 +53,7 @@ def print_ast(lang_module, input_file):
   lang_module.end_file()
 if __name__ == '__main__':
   import sys
+
   lang = sys.argv[1]
   filename = sys.argv[2]
 
diff --git a/ast/c.py b/ast/c.py
index 836a67d..5d2b6ac 100644
--- a/ast/c.py
+++ b/ast/c.py
@@ -2,7 +2,7 @@
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
-
+from __future__ import print_function
 from casing import snake
 
 from license import C_LICENSE_COMMENT
@@ -60,7 +60,7 @@ def __init__(self):
     self._current_type = None
 
   def start_file(self):
-    print C_LICENSE_COMMENT + '''/** @generated */
+    print(C_LICENSE_COMMENT + '''/** @generated */
 
 #pragma once
 
@@ -68,33 +68,33 @@ def start_file(self):
 extern "C" {
 #endif
 
-'''
+''')
 
   def end_file(self):
-    print '''
+    print('''
 
 #ifdef __cplusplus
 }
 #endif
-'''
+''')
 
   def start_type(self, name):
     # Forward declarations for AST nodes.
     st_name = struct_name(name)
-    print 'struct ' + st_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) + ';'
+    print(field_prototype(self._current_type, type, name, nullable, plural) + ';')
 
   def end_type(self, name):
-    print
+    print()
 
   def start_union(self, name):
-    print 'struct ' + struct_name(name) + ';'
+    print('struct ' + struct_name(name) + ';')
 
   def union_option(self, option):
     pass
 
   def end_union(self, name):
-    print
+    print()
diff --git a/ast/c_impl.py b/ast/c_impl.py
index 5ff3c30..bfc1d68 100644
--- a/ast/c_impl.py
+++ b/ast/c_impl.py
@@ -2,6 +2,7 @@
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
+from __future__ import print_function
 
 from c import field_prototype, return_type, struct_name
 from casing import title
@@ -15,13 +16,13 @@ def __init__(self):
     self._current_type = None
 
   def start_file(self):
-    print C_LICENSE_COMMENT + '''/** @generated */
+    print(C_LICENSE_COMMENT + '''/** @generated */
 
 #include "GraphQLAst.h"
 #include "../Ast.h"
 
 using namespace facebook::graphql::ast;  // NOLINT
-'''
+''')
 
   def end_file(self):
     pass
@@ -30,23 +31,23 @@ 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
+    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)
+        print('  return %s ? %s->size() : 0;' % (call_get, call_get))
       else:
-        print '  return %s.size();' % call_get
+        print('  return %s.size();' % call_get)
     else:
       if type in ['string', 'OperationKind', 'boolean']:
-        print '  return %s;' % call_get
+        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(fmt % (struct_name(type), '' if nullable else '&', call_get))
 
-    print '}'
+    print('}')
 
   def end_type(self, name):
     pass
diff --git a/ast/c_visitor_impl.py b/ast/c_visitor_impl.py
index aac56b2..ff91a30 100644
--- a/ast/c_visitor_impl.py
+++ b/ast/c_visitor_impl.py
@@ -2,7 +2,7 @@
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
-
+from __future__ import print_function
 from casing import snake
 from license import C_LICENSE_COMMENT
 
@@ -14,8 +14,8 @@ def __init__(self):
     self._types = []
 
   def start_file(self):
-    print C_LICENSE_COMMENT + '/** @generated */'
-    print '#define FOR_EACH_CONCRETE_TYPE(MACRO) \\'
+    print(C_LICENSE_COMMENT + '/** @generated */')
+    print('#define FOR_EACH_CONCRETE_TYPE(MACRO) \\')
 
   def start_type(self, name):
     self._types.append(name)
@@ -27,7 +27,7 @@ def end_type(self, name):
     pass
 
   def end_file(self):
-    print ' \\\n'.join('MACRO(%s, %s)' % (name, snake(name)) for name in self._types)
+    print(' \\\n'.join('MACRO(%s, %s)' % (name, snake(name)) for name in self._types))
 
   def start_union(self, name):
     pass
diff --git a/ast/cxx.py b/ast/cxx.py
index 81a1bf5..aa0f9c1 100644
--- a/ast/cxx.py
+++ b/ast/cxx.py
@@ -2,8 +2,11 @@
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
-
-import cStringIO as StringIO
+from __future__ import print_function
+try:
+    import cStringIO as StringIO
+except ImportError:
+    import io as StringIO
 
 from casing import title
 from license import C_LICENSE_COMMENT
@@ -21,7 +24,7 @@ def __init__(self):
     self._fields = []
 
   def start_file(self):
-    print C_LICENSE_COMMENT + '''/** @generated */
+    print(C_LICENSE_COMMENT + '''/** @generated */
 #pragma once
 
 #include "AstNode.h"
@@ -40,14 +43,14 @@ def start_file(self):
 struct CDeleter {
   void operator()(const char *p) const { free((void *)p); }
 };
-'''
+''')
 
   def end_file(self):
-    print
-    print self._deferredOutput.getvalue()
-    print '}'
-    print '}'
-    print '}'
+    print()
+    print(self._deferredOutput.getvalue())
+    print('}')
+    print('}')
+    print('}')
 
   def _base_class(self, type):
     return self._bases.get(type, 'Node')
@@ -56,8 +59,8 @@ def start_type(self, name):
     self._type_name = name
     base = self._base_class(name)
     # non-deferred!
-    print 'class %s;' % name
-    print >> self._deferredOutput, 'class %s : public %s {' % (name, base)
+    print('class %s;' % name)
+    print('class %s : public %s {' % (name, base), file=self._deferredOutput)
     self._fields = []
 
   def field(self, type, name, nullable, plural):
@@ -67,18 +70,18 @@ def field(self, type, name, nullable, plural):
 
   def end_type(self, name):
     self._print_fields()
-    print >> self._deferredOutput, ' public:'
+    print(' public:', file=self._deferredOutput)
     self._print_constructor()
-    print >> self._deferredOutput
+    print(file=self._deferredOutput)
     self._print_destructor_prototype()
-    print >> self._deferredOutput
+    print(file=self._deferredOutput)
     self._print_noncopyable()
-    print >> self._deferredOutput
+    print(file=self._deferredOutput)
     self._print_getters()
-    print >> self._deferredOutput, '  void accept(visitor::AstVisitor *visitor) const override;'
-    print >> self._deferredOutput, '};'
-    print >> self._deferredOutput
-    print >> self._deferredOutput
+    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 = []
 
@@ -95,7 +98,7 @@ def _print_fields(self):
       storage_type = self._storage_type(type)
       if plural:
         storage_type = 'std::unique_ptr<std::vector<%s>>' % storage_type
-      print >> self._deferredOutput, '  %s %s_;' % (storage_type, name)
+      print('  %s %s_;' % (storage_type, name), file=self._deferredOutput)
 
   def _ctor_singular_type(self, type):
     if type == 'string':
@@ -109,28 +112,28 @@ def _ctor_plural_type(self, type):
     return 'std::vector<%s> *' % self._storage_type(type)
 
   def _print_constructor(self):
-    print >> self._deferredOutput, '  explicit %s(' % self._type_name
-    print >> self._deferredOutput, '      const yy::location &location%s' % (',' if self._fields else '')
+    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 >> self._deferredOutput, ',\n'.join(ctor_arg(type, name, plural)
-                     for (type, name, nullable, plural) in self._fields)
-    print >> self._deferredOutput, '  )'
+    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 >> self._deferredOutput, '  : %s(location)%s' % (self._base_class(self._type_name), ',' if self._fields else '')
-    print >> self._deferredOutput, ',\n'.join(ctor_init(type, name, plural)
+    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)
-    print >> self._deferredOutput, '  {}'
+                     in self._fields), file=self._deferredOutput)
+    print('  {}', file=self._deferredOutput)
 
   def _getter_type(self, type, nullable, plural):
     if plural and nullable:
@@ -163,31 +166,31 @@ def _getter_value_to_return(self, raw_value, type, nullable, plural):
 
   def _print_getters(self):
     for (type, name, nullable, plural) in self._fields:
-      print >> self._deferredOutput, '  %s get%s() const' % (
+      print('  %s get%s() const' % (
         self._getter_type(type, nullable, plural),
-        title(name))
-      print >> self._deferredOutput, '  { return %s; }' % (
-        self._getter_value_to_return(name + '_', type, nullable, plural))
-      print >> self._deferredOutput
+        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 >> self._deferredOutput, '  ~%s() {}' % self._type_name
+    print('  ~%s() {}' % self._type_name, file=self._deferredOutput)
 
   def _print_noncopyable(self):
-    print >> self._deferredOutput, '  %s(const %s&) = delete;' % (
-      self._type_name, self._type_name)
-    print >> self._deferredOutput, '  %s& operator=(const %s&) = delete;' % (
-      self._type_name, self._type_name)
-  
+    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 >> self._deferredOutput, 'class %s : public Node {' % name
-    print >> self._deferredOutput, ' public:'
+    print('class %s;' % name)
+    print('class %s : public Node {' % name, file=self._deferredOutput)
+    print(' public:', file=self._deferredOutput)
     self._print_constructor()
-    print >> self._deferredOutput, '};'
-    print >> self._deferredOutput
+    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
diff --git a/ast/cxx_impl.py b/ast/cxx_impl.py
index 7f1b989..60ea325 100644
--- a/ast/cxx_impl.py
+++ b/ast/cxx_impl.py
@@ -2,7 +2,7 @@
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
-
+from __future__ import print_function
 from license import C_LICENSE_COMMENT
 
 class Printer(object):
@@ -10,7 +10,7 @@ def __init__(self):
     pass
 
   def start_file(self):
-    print C_LICENSE_COMMENT + '''/** @generated */
+    print(C_LICENSE_COMMENT + '''/** @generated */
 
 #include "Ast.h"
 #include "AstVisitor.h"
@@ -18,38 +18,38 @@ def start_file(self):
 namespace facebook {
 namespace graphql {
 namespace ast {
-'''
+''')
 
   def end_file(self):
-    print '}  // namespace ast'
-    print '}  // namespace graphql'
-    print '}  // namespace facebook'
+    print('}  // namespace ast')
+    print('}  // namespace graphql')
+    print('}  // namespace facebook')
 
   def start_type(self, name):
-    print '''void %s::accept(visitor::AstVisitor *visitor) const {
+    print('''void %s::accept(visitor::AstVisitor *visitor) const {
   if (visitor->visit%s(*this)) {
-''' % (name, name)
+''' % (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
+      print('    ' + accept)
     else:
       accept = '%s_->accept(visitor);' % name
       if nullable:
         accept = 'if (%s_) { %s }' % (name, accept)
-      print '    ' + accept
+      print('    ' + accept)
 
   def end_type(self, name):
-    print '''  }
+    print('''  }
   visitor->endVisit%s(*this);
 }
-''' % name
+''' % name)
 
   def start_union(self, name):
     pass
diff --git a/ast/cxx_json_visitor_header.py b/ast/cxx_json_visitor_header.py
index 2f8a02a..0e37679 100644
--- a/ast/cxx_json_visitor_header.py
+++ b/ast/cxx_json_visitor_header.py
@@ -3,7 +3,7 @@
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
-
+from __future__ import print_function
 from casing import title
 from license import C_LICENSE_COMMENT
 
@@ -12,7 +12,7 @@ def __init__(self):
     self._anyFieldIsANode = False
 
   def start_file(self):
-    print C_LICENSE_COMMENT + '/** @generated */'
+    print(C_LICENSE_COMMENT + '/** @generated */')
 
   def end_file(self):
     pass
@@ -23,9 +23,9 @@ def start_type(self, name):
   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
+      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
diff --git a/ast/cxx_json_visitor_impl.py b/ast/cxx_json_visitor_impl.py
index db8f9ab..91d2548 100644
--- a/ast/cxx_json_visitor_impl.py
+++ b/ast/cxx_json_visitor_impl.py
@@ -3,7 +3,7 @@
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
-
+from __future__ import print_function
 from casing import title
 from license import C_LICENSE_COMMENT
 
@@ -12,7 +12,7 @@ def __init__(self):
     self._fields = []
 
   def start_file(self):
-    print C_LICENSE_COMMENT + '/** @generated */'
+    print(C_LICENSE_COMMENT + '/** @generated */')
 
   def end_file(self):
     pass
@@ -30,13 +30,13 @@ def end_type(self, name):
     anyFieldIsANode = any(type not in ('string, boolean')
                           for (type, _, _ ,_) in self._fields)
     if anyFieldIsANode:
-      print '''bool JsonVisitor::visit%s(const %s &node) {
+      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}
+''' % (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
@@ -48,7 +48,7 @@ def end_type(self, name):
         funcName = 'printSingularBooleanField'
       elif not nullable and not plural:
         # Special case: singular object fields don't need the value passed.
-        print '  fields.printSingularObjectField("%s");' % fieldName
+        print('  fields.printSingularObjectField("%s");' % fieldName)
         continue
       else:
         nullable_str = 'Nullable' if nullable else ''
@@ -56,19 +56,19 @@ def end_type(self, name):
         funcName = 'print%s%sField' % (nullable_str, plural_str)
 
       assert funcName is not None
-      print '  fields.%s("%s", node.get%s());' % (
-        funcName, fieldName, title(fieldName))
+      print('  fields.%s("%s", node.get%s());' % (
+        funcName, fieldName, title(fieldName)))
 
     if anyFieldIsANode:
-      print '''
+      print('''
   endVisitNode(fields.finishPrinting());
 }
-'''
+''')
     else:
-      print '''
+      print('''
   printed_.back().emplace_back(fields.finishPrinting());
 }
-'''
+''')
 
   def start_union(self, name):
     pass
diff --git a/ast/cxx_visitor.py b/ast/cxx_visitor.py
index 91aa0b5..cbbfbc0 100644
--- a/ast/cxx_visitor.py
+++ b/ast/cxx_visitor.py
@@ -2,7 +2,7 @@
 #
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
-
+from __future__ import print_function
 from casing import camel, title
 from license import C_LICENSE_COMMENT
 
@@ -11,7 +11,7 @@ def __init__(self):
     pass
 
   def start_file(self):
-    print C_LICENSE_COMMENT + '''/** @generated */
+    print(C_LICENSE_COMMENT + '''/** @generated */
 
 #pragma once
 
@@ -25,28 +25,28 @@ def start_file(self):
 class AstVisitor {
 public:
   virtual ~AstVisitor() {}
-'''
+''')
 
   def end_file(self):
-    print '};' # end AstVisitor
-    print
-    print '}'
-    print '}'
-    print '}'
-    print '}'
+    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; }' % (
+    print('  virtual bool visit%s(const %s &%s) { return true; }' % (
       titleName,
       titleName,
-      camelName)
-    print '  virtual void endVisit%s(const %s &%s) { }' % (
+      camelName))
+    print('  virtual void endVisit%s(const %s &%s) { }' % (
       titleName,
       titleName,
-      camelName)
-    print
+      camelName))
+    print()
 
   def end_type(self, name):
     pass
diff --git a/ast/js.py b/ast/js.py
index cb6c023..143d828 100644
--- a/ast/js.py
+++ b/ast/js.py
@@ -3,13 +3,13 @@
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
 
-
+from __future__ import print_function
 class Printer(object):
   def __init__(self):
     pass
 
   def start_file(self):
-    print '''/* @flow */
+    print('''/* @flow */
 /* @generated */
 /* jshint ignore:start */
 
@@ -26,21 +26,21 @@ def start_file(self):
   end?: ?number;
 };
 
-type OperationKind = 'query' | 'mutation' | 'subscription';'''
+type OperationKind = 'query' | 'mutation' | 'subscription';''')
 
   def end_file(self):
     pass
 
   def start_type(self, name):
-    print
-    print 'type %s = Node & {' % name
+    print()
+    print('type %s = Node & {' % name)
     kind = name
     if kind == 'GenericType':
       kind = 'Type'
-    print '  kind: \'%s\';' % kind
+    print('  kind: \'%s\';' % kind)
 
   def end_type(self, name):
-    print '}'
+    print('}')
 
   def _js_type(self, type, plural):
     if plural:
@@ -50,16 +50,16 @@ def _js_type(self, type, plural):
   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()
+    print('  %(name)s%(nullable_char)s: %(nullable_char)s%(js_type)s;' % locals())
 
   def start_union(self, name):
-    print ('type %s = ' % 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
+    print('\n  | '.join(self._current_options))
+    print()
     self._current_options = None
diff --git a/parser.ypp b/parser.ypp
index 591e885..b425926 100644
--- a/parser.ypp
+++ b/parser.ypp
@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  */
 
-%require "3"
+/* %require "3" */
 
 %skeleton "lalr1.cc"
 
@@ -278,7 +278,7 @@ union yystype {                                         \
 %type <typeNameList> union_members;
 %type <fieldDefinition> field_definition;
 %type <fieldDefinitionList> field_definition_list;
-%type <inputValueDefinitionList> arguments_definition_opt; 
+%type <inputValueDefinitionList> arguments_definition_opt;
 %type <inputValueDefinitionList> arguments_definition;
 %type <inputValueDefinitionList> input_value_definition_list;
 %type <inputValueDefinition> input_value_definition;
@@ -333,7 +333,7 @@ name_opt:
 
 document:       definition_list { $$ = new Document(@$, $1); }
         ;
-                
+
 definition_list:definition { $$ = new std::vector<std::unique_ptr<Definition>>(); $$->emplace_back($1); }
         |       definition_list definition { $1->emplace_back($2); $$ = $1; }
         ;