[context] Split "env" values and prefixes.

recipe_modules/python/api.py

 # Copyright 2013 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 import textwrap
 
 from recipe_engine import config_types
 from recipe_engine import recipe_api
 
 class PythonApi(recipe_api.RecipeApi):
@@ skipping 13 matching lines @@
           Python command.
       unbuffered (bool): If True, run Python in unbuffered mode.
       venv (None or False or True or Path): If True, run the script through
           "vpython". This will, by default, probe the target script for a
           configured VirtualEnv and, failing that, use an empty VirtualEnv. If a
           Path, this is a path to an explicit "vpython" VirtualEnv spec file to
           use. If False or None (default), the script will be run through the
           standard Python interpreter.
       kwargs: Additional keyword arguments to forward to "step".
     """
-    env = self.m.context.env
+    env = {}
 
     if venv:
       cmd = ['vpython']
       if isinstance(venv, config_types.Path):
         cmd += ['-spec', venv]
     else:
       cmd = ['python']
 
     if unbuffered:
       cmd.append('-u')
     else:
       env['PYTHONUNBUFFERED'] = None
 
-    context = {}
-    if env:
-      context['env'] = env
-
     cmd.append(script)
-    with self.m.context(**context):
+    with self.m.context(env=env):
       return self.m.step(name, cmd + list(args or []), **kwargs)
 
   def inline(self, name, program, add_python_log=True, **kwargs):
     """Run an inline python program as a step.
 
     Program is output to a temp file and run when this step executes.
     """
     program = textwrap.dedent(program)
     compile(program, '<string>', 'exec', dont_inherit=1)
 
@@ skipping 21 matching lines @@
       else:
         self.m.step.active_result.presentation.step_text = text
 
   def succeeding_step(self, name, text, as_log=None):
     """Return a succeeding step (correctly recognized in expectations)."""
     return self.result_step(name, text, 0, as_log=as_log)
 
   def failing_step(self, name, text, as_log=None):
     """Return a failing step (correctly recognized in expectations)."""
     return self.result_step(name, text, 1, as_log=as_log)