initial pushshift/rexport merge implementation

my/core/cfg.py

@@ -10,7 +10,7 @@ C = TypeVar('C')
 def make_config(cls: Type[C], migration: Callable[[Attrs], Attrs]=lambda x: x) -> C:
     user_config = cls.__base__
     old_props = {
-        # NOTE: deliberately use gettatr to 'force' lcass properties here
+        # NOTE: deliberately use gettatr to 'force' class properties here
         k: getattr(user_config, k) for k in vars(user_config)
     }
     new_props = migration(old_props)

my/core/source.py

@@ -0,0 +1,26 @@
+from typing import Any, Iterator, TypeVar, Callable, Optional, Iterable
+from my.core.warnings import warn
+
+T = TypeVar("T")
+
+# this is probably more generic and results in less code, but is not mypy-friendly
+def import_source(factory: Callable[[], Any], default: Any) -> Any:
+    try:
+        res = factory()
+        return res
+    except ImportError: # presumable means the user hasn't installed the module
+        warn(f"Module {factory.__name__} could not be imported, or isn't configured propertly")
+        return default
+
+
+# For an example of this, see the reddit.all file
+def import_source_iter(factory: Callable[[], Iterator[T]], default: Optional[Iterable[T]] = None) -> Iterator[T]:
+    if default is None:
+        default = []
+    try:
+        res = factory()
+        yield from res
+    except ImportError: # presumable means the user hasn't installed the module
+        warn(f"Module {factory.__name__} could not be imported, or isn't configured propertly")
+        yield from default
+