config adapter helper functions (#896)

Summary:
Pull Request resolved: #896

config adapter has a very powerfull function `rename_parameter`.
This diff splits this function to expose its inner functions that can be
useful for more than just renaming parameters.

These new functions will be used in the next diff in the stack

Reviewed By: bethebunny

Differential Revision: D16749189

fbshipit-source-id: 3e9c9e0eb0e977d8392e3239101e4a17e1b2039b

pytext/config/config_adapter.py

@@ -6,6 +6,7 @@
 
 
 ADAPTERS = {}
+NOT_THERE = (None, None, None)
 
 
 def register_adapter(from_version):
@@ -49,7 +50,51 @@ def is_type_specifier(json_dict):
     return key[0] == key[0].upper()
 
 
-def rename_parameter(config, old_path, new_path):
+def find_parameter(config, path_str):
+    # Recursively find path elements, skipping into type specifiers.
+    # Return the value and its container so the value can be deleted.
+
+    path = path_str.split(".")
+    value = config
+    container = None
+    for segment in path:
+        while is_type_specifier(value):
+            container, value = value, next(iter(value.values()))
+        if segment not in value:
+            return NOT_THERE
+        container, value = value, value[segment]
+    return path[-1], container, value
+
+
+def _create_path(config, path):
+    # Recursively find path elements, skipping into type specifiers.
+    # If any container isn't there, create a new empty object for it.
+    # This will only be created if the
+    value = config
+    for segment in path:
+        while is_type_specifier(value):
+            value = next(iter(value.values()))
+        if segment not in value:
+            value[segment] = {}
+        value = value[segment]
+    while is_type_specifier(value):
+        value = next(iter(value.values()))
+    return value
+
+
+def create_parameter(config, path_str, value):
+    *path, param = path_str.split(".")
+    new_container = _create_path(config, path)
+    new_container[param] = value
+
+
+def delete_parameter(config, path_str):
+    param_name, container, _ = find_parameter(config, path_str)
+    if container:
+        container.pop(param_name, None)
+
+
+def rename_parameter(config, old_path, new_path, transform=lambda x: x):
     """A powerful tool for writing config adapters, this allows you to specify
     a JSON-style path for an old and new config parameter. For instance
 
@@ -60,47 +105,13 @@ def rename_parameter(config, old_path, new_path):
     set it in task.trainer.num_batches_per_epoch instead, creating trainer as an empty
     dictionary if necessary."""
 
-    old_path = old_path.split(".")
-    new_path = new_path.split(".")
-
-    NOT_THERE = object()
-
-    def find_path(config, path):
-        # Recursively find path elements, skipping into type specifiers.
-        # Return the value and its container so the value can be deleted.
-        value = config
-        container = None
-        for segment in path:
-            while is_type_specifier(value):
-                container, value = value, next(iter(value.values()))
-            if segment not in value:
-                return NOT_THERE
-            container, value = value, value[segment]
-        return container, value
-
-    def create_path(config, path):
-        # Recursively find path elements, skipping into type specifiers.
-        # If any container isn't there, create a new empty object for it.
-        # This will only be created if the
-        value = config
-        for segment in path:
-            while is_type_specifier(value):
-                value = next(iter(value.values()))
-            if segment not in value:
-                value[segment] = {}
-            value = value[segment]
-        while is_type_specifier(value):
-            value = next(iter(value.values()))
-        return value
-
-    found = find_path(config, old_path)
+    found = find_parameter(config, old_path)
     if found is not NOT_THERE:
-        container, old_value = found
+        param_name, container, old_value = found
         # Delete old value
-        container.pop(old_path[-1])
+        container.pop(param_name)
         # Update new value
-        new_container = create_path(config, new_path[:-1])
-        new_container[new_path[-1]] = old_value
+        create_parameter(config, new_path, transform(old_value))
 
     return config