diff --git a/mycpp/cppgen_pass.py b/mycpp/cppgen_pass.py
index 001bc441a2..bd82364b67 100644
--- a/mycpp/cppgen_pass.py
+++ b/mycpp/cppgen_pass.py
@@ -52,6 +52,9 @@ def get_c_type(t):
       inner_c_type = get_c_type(type_param)
       c_type = 'List<%s>*' % inner_c_type
 
+    elif type_name == 'typing.IO':
+      c_type = 'runtime::IO*'
+
     else:
       # fullname() => 'parse.Lexer'; name() => 'Lexer'
 
@@ -283,7 +286,9 @@ def visit_member_expr(self, o: 'mypy.nodes.MemberExpr') -> T:
         if o.expr:  
           # This is an approximate hack that assumes that locals don't shadow
           # imported names.  Might be a problem with names like 'word'?
-          if isinstance(o.expr, NameExpr) and o.expr.name in self.imported_names:
+          expr_name = o.expr.name
+          if (isinstance(o.expr, NameExpr) and
+             (expr_name in self.imported_names or expr_name == 'runtime')):
             op = '::'
           else:
             op = '->'  # Everything is a pointer
@@ -331,9 +336,7 @@ def visit_call_expr(self, o: 'mypy.nodes.CallExpr') -> T:
             self.write('new ')
 
         # Namespace.
-        if callee_name == 'Buf':
-          self.write('runtime::Buf')
-        elif callee_name == 'int':  # int('foo') in Python conflicts with keyword
+        if callee_name == 'int':  # int('foo') in Python conflicts with keyword
           self.write('str_to_int')
         else:
           self.accept(o.callee)  # could be f() or obj.method()
diff --git a/mycpp/examples/files.py b/mycpp/examples/files.py
index a534bcec9e..1622d17df9 100755
--- a/mycpp/examples/files.py
+++ b/mycpp/examples/files.py
@@ -7,13 +7,14 @@
 import os
 import sys
 
-from runtime import log, Buf
+import runtime
+from runtime import log
 
 
 def run_tests():
   # type: () -> None
 
-  f = Buf()
+  f = runtime.Buf()
   for i in xrange(30):
     f.write(chr(i + 65))
 
@@ -21,9 +22,8 @@ def run_tests():
   log('Wrote %d bytes to StringIO', len(contents))
   log('contents = %s ... %s', contents[:10], contents[-10:])
 
-  # TODO:
-  #f = sys.stdout
-  #f.write('stdout\n')
+  f2 = runtime.StdOut()
+  f2.write('stdout\n')
 
 
 def run_benchmarks():
@@ -34,7 +34,7 @@ def run_benchmarks():
 
   i = 0
   while i < n:
-    f = Buf()
+    f = runtime.Buf()
     for j in xrange(30):
       f.write(chr(i + 65))
 
diff --git a/mycpp/run.sh b/mycpp/run.sh
index 8fe69ff74f..2767190830 100755
--- a/mycpp/run.sh
+++ b/mycpp/run.sh
@@ -313,7 +313,7 @@ python-example() {
 example-both() {
   local name=$1
 
-  #mypy --py2 --strict examples/$name.py
+  mypy --py2 --strict examples/$name.py
 
   translate-example $name
   compile-example $name
diff --git a/mycpp/runtime.cc b/mycpp/runtime.cc
index 3e2ebc3998..4554fd4a17 100644
--- a/mycpp/runtime.cc
+++ b/mycpp/runtime.cc
@@ -143,20 +143,25 @@ Str* StrIter::Value() {
 
 namespace runtime {
 
+IO* gStdOut;
+
 void Buf::write(Str* s) {
   int orig_len = len_;
   len_ += s->len_;
-  if (data_ == nullptr) {  // first write
-    data_ = static_cast<char*>(malloc(len_ + 1));
-  } else {
-    data_ = static_cast<char*>(realloc(data_, len_ + 1));
-  }
+  // data_ is nullptr at first
+  data_ = static_cast<char*>(realloc(data_, len_ + 1));
 
   // Append to the end
   memcpy(data_ + orig_len, s->data_, s->len_);
   data_[len_] = '\0';
 }
 
+void CFile::write(Str* s) {
+  // note: throwing away the return value
+  fwrite(s->data_, s->len_, 1, f_);
+}
+
+
 };
 
 //
diff --git a/mycpp/runtime.h b/mycpp/runtime.h
index ae039ed344..ff8ee1db3a 100644
--- a/mycpp/runtime.h
+++ b/mycpp/runtime.h
@@ -8,6 +8,8 @@
 #include <stddef.h>  // size_t
 #include <stdlib.h>  // malloc
 #include <string.h>  // strlen
+// https://stackoverflow.com/questions/3882346/forward-declare-file
+#include <cstdio>  // FILE*
 #include <vector>
 #include <initializer_list>
 
@@ -297,11 +299,16 @@ int str_to_int(Str* s);
 
 namespace runtime {  // MyPy artifact
 
-class Buf {
+class IO {
+ public:
+  virtual void write(Str* s) = 0;
+};
+
+class Buf : public IO {
  public:
   Buf() : data_(nullptr), len_(0) {
   };
-  void write(Str* s);
+  virtual void write(Str* s);
   Str* getvalue() { return new Str(data_, len_); }
 
  private:
@@ -310,6 +317,26 @@ class Buf {
   size_t len_;
 };
 
+// Wrap a FILE*
+class CFile : public IO {
+ public:
+  CFile(FILE* f) : f_(f) {
+  };
+  virtual void write(Str* s);
+
+ private:
+  FILE* f_;
+};
+
+extern IO* gStdOut;
+
+inline IO* StdOut() {
+  if (gStdOut == nullptr) {
+    gStdOut = new CFile(stdout);
+  }
+  return gStdOut;
+}
+
 };
 
 #endif  // RUNTIME_H
diff --git a/mycpp/runtime.py b/mycpp/runtime.py
index 9ee9741eb4..232380bd00 100644
--- a/mycpp/runtime.py
+++ b/mycpp/runtime.py
@@ -4,7 +4,7 @@
 from __future__ import print_function
 
 import sys
-from typing import Any
+from typing import IO, Any
 
 
 # C code ignores this!
@@ -25,3 +25,7 @@ def p_die(msg, *args):
 
 class Buf(StringIO.StringIO):
   pass
+
+
+def StdOut():
+  return sys.stdout
diff --git a/mycpp/runtime.pyi b/mycpp/runtime.pyi
new file mode 100644
index 0000000000..337e9c1b3f
--- /dev/null
+++ b/mycpp/runtime.pyi
@@ -0,0 +1,9 @@
+from typing import IO, Any
+
+class Buf:
+  def write(self, s: str) -> None: ...
+  def getvalue(self) -> str: ...
+
+def StdOut() -> IO[bytes]: ...
+
+def log(msg: str, *args: Any) -> None: ...