arbitrary_subfolders: Add labscript_devices.deprecated_import_alias to declare when a device

class has moved, providing the ability to still import it under the old
name whilst printing a deprecation warning pointing to the new name.
Use this function in DummyPseudoclock/__init__.py.

Author: chrisjbillington

DummyPseudoclock/__init__.py

@@ -15,4 +15,10 @@
 if PY2:
     str = unicode
 
-from .labscript_device import DummyPseudoclock
+from labscript_devices import deprecated_import_alias
+
+
+# For backwards compatibility with old experiment scripts:
+DummyPseudoclock = deprecated_import_alias(
+    "labscript_devices.DummyPseudoclock.labscript_device.DummyPseudoclock"
+)

__init__.py

@@ -159,6 +159,26 @@ def _import_class_by_fullname(fullname):
     return getattr(module, class_name)
 
 
+def deprecated_import_alias(fullname):
+    """A way of allowing a class to be imported from an old location whilst a) not
+    actually importing it until it is instantiated and b) emitting a warning pointing to
+    the new import location. fullname must be a fully qualified class name with an
+    absolute import path. Use by calling in the module where the class used to be:
+    ClassName = deprecated_import_alias("new.path.to.ClassName")"""
+    calling_module_name = inspect.getmodule(inspect.stack()[1][0]).__name__
+    def wrapper(*args, **kwargs):
+        cls = _import_class_by_fullname(fullname)
+        shortname = fullname.split('.')[-1]
+        newmodule = '.'.join(fullname.split('.')[:-1])
+        msg = """Importing %s from %s is deprecated, please instead import it from %s.
+           Importing anyway for backward compatibility, but this may cause some
+           unexpected behaviour."""
+        msg = dedent(msg) % (shortname, calling_module_name, newmodule)
+        warnings.warn(msg, stacklevel=2)
+        return cls(*args, **kwargs)
+    return wrapper
+
+
 # Dictionaries containing the import paths to BLACS tab and runviewer parser classes,
 # not the classes themselves. These will be populated by calls to register_classes from
 # code within register_classes.py files within subfolders of labscript_devices.