Split Placeholder into InputPlaceholder and OutputPlaceholder.

recipe_engine/util.py

 # Copyright 2013-2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import contextlib
 import functools
 import os
 import sys
 import traceback
 import urllib
@@ skipping 16 matching lines @@
     if self.owner_module is None:
       raise ModuleInjectionError(
         "RecipeApi has no dependency %r. (Add it to DEPS?)" % (key,))
     else:
       raise ModuleInjectionError(
         "Recipe Module %r has no dependency %r. (Add it to __init__.py:DEPS?)"
         % (self.owner_module.name, key))
 
 
 class Placeholder(object):
-  """Base class for json placeholders. Do not use directly."""
+  """Base class for command line argument placeholders. Do not use directly."""
   def __init__(self):
     self.name_pieces = None
 
   @property
   def backing_file(self):  # pragma: no cover
     """Return path to a temp file that holds or receives the data.
 
     Valid only after 'render' has been called.
     """
     raise NotImplementedError
 
   def render(self, test):  # pragma: no cover
     """Return [cmd items]*"""
     raise NotImplementedError
 
   def result(self, presentation, test):
     """Called after step completion.
 
     Args:
       presentation (StepPresentation) - for the current step.
       test (PlaceholderTestData) - test data for this placeholder.
 
-    Returns value to add to step result.
-
     May optionally modify presentation as a side-effect.
     """
     pass
 
   @property
   def name(self):
     assert self.name_pieces
     return "%s.%s" % self.name_pieces
 
 
+class InputPlaceholder(Placeholder):
+  """Base class for json/raw_io input placeholders. Do not use directly."""
+  def result(self, presentation, test):
+    """Returned value will be discarded."""
+    pass
+  result.__doc__ = Placeholder.result.__doc__
+
+
+class OutputPlaceholder(Placeholder):
+  """Base class for json/raw_io output placeholders. Do not use directly."""
+  def result(self, presentation, test):
+    """Returned value will be added to the step result."""
+    pass
+  result.__doc__ = Placeholder.result.__doc__
+
+
 def static_wraps(func):
   wrapped_fn = func
   if isinstance(func, staticmethod):
     # __get__(obj) is the way to get the function contained in the staticmethod.
     # python 2.7+ has a __func__ member, but previous to this the attribute
     # doesn't exist. It doesn't matter what the obj is, as long as it's not
     # None.
     wrapped_fn = func.__get__(object)
   return functools.wraps(wrapped_fn)
 
@@ skipping 82 matching lines @@
         self.lines[-1].write(s)
         break
       self.lines[-1].write(s[:i])
       self.lines[-1] = self.lines[-1].getvalue()
       self.lines.append(StringIO())
       s = s[i+1:]
 
   def close(self):
     if not isinstance(self.lines[-1], basestring):
       self.lines[-1] = self.lines[-1].getvalue()