first draft of a pre_run feature

examples/pre_run.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python
+# coding=utf-8
+from __future__ import division, print_function, unicode_literals
+from sacred import Experiment
+
+ex = Experiment('hello_config_scope')
+
+
+# A ConfigScope is a function like this decorated with @ex.config
+# All local variables of this function will be put into the configuration
+@ex.config
+def cfg():
+    recipient = "world"
+    message = "Hello %s!" % recipient
+
+
+@ex.pre_run
+def foobar(command_name, config_updates, named_configs):
+    print('FOOOOBAR:', command_name)
+    config_updates['recipient'] = 'FOOO'
+    return command_name, config_updates, named_configs
+
+
+# again we can access the message here by taking it as an argument
+@ex.automain
+def main(message):
+    print(message)

sacred/experiment.py

@@ -34,6 +34,7 @@ class Ingredient(object):
     def __init__(self, path, ingredients=(), _generate_seed=False,
                  _caller_globals=None):
         self.path = path
+        self._pre_run = None
         self.cfgs = []
         self.named_configs = dict()
         self.ingredients = list(ingredients)
@@ -49,6 +50,12 @@ def __init__(self, path, ingredients=(), _generate_seed=False,
         self.current_run = None
 
     # =========================== Decorators ==================================
+    def pre_run(self, func):
+        if self._pre_run is None:
+            self._pre_run = func
+        else:
+            raise RuntimeError('Can only have one pre_run!')
+
     def command(self, function=None, prefix=None):
         """
         Decorator to define a new command for this Ingredient or Experiment.

sacred/initialize.py

@@ -214,8 +214,7 @@ def initialize_logging(experiment, scaffolding, loglevel=None):
     return root_logger.getChild(experiment.name)
 
 
-def create_scaffolding(experiment):
-    sorted_ingredients = gather_ingredients_topological(experiment)
+def create_scaffolding(experiment, sorted_ingredients):
     scaffolding = OrderedDict()
     for ingredient in sorted_ingredients:
         scaffolding[ingredient] = Scaffold(
@@ -259,9 +258,23 @@ def get_command(scaffolding, command_path):
             raise KeyError('Command "%s" not found' % command_name)
 
 
+def execute_pre_runs(ingredients, command_name, config_updates, named_configs):
+    args = (command_name, config_updates, named_configs)
+    for ingred in ingredients:
+        if ingred._pre_run:
+            args = ingred._pre_run(*args)
+    return args
+
+
 def create_run(experiment, command_name, config_updates=None, log_level=None,
                named_configs=()):
-    scaffolding = create_scaffolding(experiment)
+
+    sorted_ingredients = gather_ingredients_topological(experiment)
+    scaffolding = create_scaffolding(experiment, sorted_ingredients)
+
+    command_name, config_updates, named_configs = \
+        execute_pre_runs(sorted_ingredients, command_name, config_updates,
+                         named_configs)
 
     distribute_config_updates(scaffolding, config_updates)
     distribute_named_configs(scaffolding, named_configs)