Merge pull request #2544 from astrofrog/override-defaults

Allow initial values to be customized for state classes

Author: astrofrog

glue/core/state_objects.py

@@ -1,6 +1,7 @@
 from textwrap import indent
 
 from collections import defaultdict
+from contextlib import contextmanager
 
 import numpy as np
 
@@ -13,6 +14,7 @@
 from glue.core.exceptions import IncompatibleAttribute
 from glue.core.units import UnitConverter
 
+
 __all__ = ['State', 'StateAttributeCacheHelper',
            'StateAttributeLimitsHelper', 'StateAttributeSingleValueHelper', 'StateAttributeHistogramHelper']
 
@@ -27,6 +29,36 @@ def _load_callback_list(rec, context):
     return [context.object(obj) for obj in rec['values']]
 
 
+_state_default_picker = None
+
+
+def set_state_default_picker(func):
+    """
+    This function can be used to set a function that will be used
+    to override default values in state classes.
+
+    The function will be called whenever a state class is being
+    initialized, and will be given the instance of the class being
+    created. The function is then free to modify any of the callback
+    properties, before any of the callbacks are set up.
+    """
+
+    global _state_default_picker
+    _state_default_picker = func
+
+
+@contextmanager
+def with_state_default_picker(func):
+    """
+    Context manager version of `set_state_default_picker`.
+    """
+
+    global _state_default_picker
+    _state_default_picker = func
+    yield
+    _state_default_picker = None
+
+
 class State(HasCallbackProperties):
     """
     A class to represent the state of a UI element. Initially this doesn't add
@@ -37,6 +69,8 @@ class State(HasCallbackProperties):
     def __init__(self, **kwargs):
         super(State, self).__init__()
         self.update_from_dict(kwargs)
+        if _state_default_picker is not None:
+            _state_default_picker(self)
 
     def update_from_state(self, state):
         """

glue/core/tests/test_state_objects.py

@@ -8,7 +8,8 @@
 from .test_state import clone
 from ..state_objects import (State, StateAttributeLimitsHelper,
                              StateAttributeSingleValueHelper,
-                             StateAttributeHistogramHelper)
+                             StateAttributeHistogramHelper,
+                             with_state_default_picker)
 
 
 class SimpleTestState(State):
@@ -532,3 +533,14 @@ class SimpleState(State):
                                         percentile='scale')
 
     state.scale = 90
+
+
+def default_picker(state):
+    if isinstance(state, SimpleTestState):
+        state.a = 5
+
+
+def test_set_state_default_picker():
+    with with_state_default_picker(default_picker):
+        state = SimpleTestState()
+        assert state.a == 5