diff --git a/Parser/asdl.py b/Parser/asdl.py
index 164ca6bd0db..74fff93a50d 100644
--- a/Parser/asdl.py
+++ b/Parser/asdl.py
@@ -204,19 +204,19 @@ class ASDLParser(spark.GenericParser, object):
 
     def p_field_2(self, (type, _, name)):
         " field ::= Id * Id "
-        return Field(type, name, seq=1)
+        return Field(type, name, seq=True)
 
     def p_field_3(self, (type, _, name)):
         " field ::= Id ? Id "
-        return Field(type, name, opt=1)
+        return Field(type, name, opt=True)
 
     def p_field_4(self, (type, _)):
         " field ::= Id * "
-        return Field(type, seq=1)
+        return Field(type, seq=True)
 
     def p_field_5(self, (type, _)):
         " field ::= Id ? "
-        return Field(type, opt=1)
+        return Field(type, opt=True)
 
 builtin_types = ("identifier", "string", "int", "bool", "object")
 
@@ -256,7 +256,7 @@ class Constructor(AST):
         return "Constructor(%s, %s)" % (self.name, self.fields)
 
 class Field(AST):
-    def __init__(self, type, name=None, seq=0, opt=0):
+    def __init__(self, type, name=None, seq=False, opt=False):
         self.type = type
         self.name = name
         self.seq = seq
@@ -264,9 +264,9 @@ class Field(AST):
 
     def __repr__(self):
         if self.seq:
-            extra = ", seq=1"
+            extra = ", seq=True"
         elif self.opt:
-            extra = ", opt=1"
+            extra = ", opt=True"
         else:
             extra = ""
         if self.name is None:
@@ -294,7 +294,7 @@ class Product(AST):
 
 class VisitorBase(object):
 
-    def __init__(self, skip=0):
+    def __init__(self, skip=False):
         self.cache = {}
         self.skip = skip
 
@@ -329,7 +329,7 @@ class VisitorBase(object):
 class Check(VisitorBase):
 
     def __init__(self):
-        super(Check, self).__init__(skip=1)
+        super(Check, self).__init__(skip=True)
         self.cons = {}
         self.errors = 0
         self.types = {}
diff --git a/Parser/asdl_c.py b/Parser/asdl_c.py
index 01597015c2b..40b84996a1b 100755
--- a/Parser/asdl_c.py
+++ b/Parser/asdl_c.py
@@ -86,7 +86,7 @@ class EmitVisitor(asdl.VisitorBase):
         self.file = file
         super(EmitVisitor, self).__init__()
 
-    def emit(self, s, depth, reflow=1):
+    def emit(self, s, depth, reflow=True):
         # XXX reflow long lines?
         if reflow:
             lines = reflow_lines(s, depth)
@@ -255,7 +255,7 @@ class PrototypeVisitor(EmitVisitor):
         ctype = get_c_type(type)
         self.emit_function(cons.name, ctype, args, attrs)
 
-    def emit_function(self, name, ctype, args, attrs, union=1):
+    def emit_function(self, name, ctype, args, attrs, union=True):
         args = args + attrs
         if args:
             argstr = ", ".join(["%s %s" % (atype, aname)
@@ -267,19 +267,19 @@ class PrototypeVisitor(EmitVisitor):
         for i in range(1, len(args)+1):
             margs += ", a%d" % i
         self.emit("#define %s(%s) _Py_%s(%s)" % (name, margs, name, margs), 0,
-                reflow = 0)
-        self.emit("%s _Py_%s(%s);" % (ctype, name, argstr), 0)
+                reflow=False)
+        self.emit("%s _Py_%s(%s);" % (ctype, name, argstr), False)
 
     def visitProduct(self, prod, name):
         self.emit_function(name, get_c_type(name),
-                           self.get_args(prod.fields), [], union=0)
+                           self.get_args(prod.fields), [], union=False)
 
 
 class FunctionVisitor(PrototypeVisitor):
     """Visitor to generate constructor functions for AST."""
 
-    def emit_function(self, name, ctype, args, attrs, union=1):
-        def emit(s, depth=0, reflow=1):
+    def emit_function(self, name, ctype, args, attrs, union=True):
+        def emit(s, depth=0, reflow=True):
             self.emit(s, depth, reflow)
         argstr = ", ".join(["%s %s" % (atype, aname)
                             for atype, aname, opt in args + attrs])
@@ -298,7 +298,7 @@ class FunctionVisitor(PrototypeVisitor):
                 emit("PyErr_SetString(PyExc_ValueError,", 2)
                 msg = "field %s is required for %s" % (argname, name)
                 emit('                "%s");' % msg,
-                     2, reflow=0)
+                     2, reflow=False)
                 emit('return NULL;', 2)
                 emit('}', 1)
 
@@ -314,7 +314,7 @@ class FunctionVisitor(PrototypeVisitor):
         emit("")
 
     def emit_body_union(self, name, args, attrs):
-        def emit(s, depth=0, reflow=1):
+        def emit(s, depth=0, reflow=True):
             self.emit(s, depth, reflow)
         emit("p->kind = %s_kind;" % name, 1)
         for argtype, argname, opt in args:
@@ -323,7 +323,7 @@ class FunctionVisitor(PrototypeVisitor):
             emit("p->%s = %s;" % (argname, argname), 1)
 
     def emit_body_struct(self, name, args, attrs):
-        def emit(s, depth=0, reflow=1):
+        def emit(s, depth=0, reflow=True):
             self.emit(s, depth, reflow)
         for argtype, argname, opt in args:
             emit("p->%s = %s;" % (argname, argname), 1)