my.reddit: refactor into module that supports pushshift/gdpr (#179)

* initial pushshift/rexport merge implementation, using id for merging
* smarter module deprecation warning using regex
* add `RedditBase` from promnesia
* `import_source` helper for gracefully handing mixin data sources

my/reddit/common.py

@@ -0,0 +1,72 @@
+"""
+This defines Protocol classes, which make sure that each different
+type of shared models have a standardized interface
+"""
+
+from typing import Dict, Any, Set, Iterator, TYPE_CHECKING
+from itertools import chain
+
+from my.core.common import datetime_aware
+
+Json = Dict[str, Any]
+
+if TYPE_CHECKING:
+    try:
+        from typing import Protocol
+    except ImportError:
+        # requirement of mypy
+        from typing_extensions import Protocol  # type: ignore[misc]
+else:
+    Protocol = object
+
+
+# common fields across all the Protocol classes, so generic code can be written
+class RedditBase(Protocol):
+    @property
+    def raw(self) -> Json: ...
+    @property
+    def created(self) -> datetime_aware: ...
+    @property
+    def id(self) -> str: ...
+    @property
+    def url(self) -> str: ...
+    @property
+    def text(self) -> str: ...
+
+
+# Note: doesn't include GDPR Save's since they don't have the same metadata
+class Save(Protocol, RedditBase):
+    @property
+    def subreddit(self) -> str: ...
+
+# Note: doesn't include GDPR Upvote's since they don't have the same metadata
+class Upvote(Protocol, RedditBase):
+    @property
+    def title(self) -> str: ...
+
+
+# From rexport, pushshift and the reddit GDPR export
+class Comment(Protocol, RedditBase):
+    pass
+
+
+# From rexport and the GDPR export
+class Submission(Protocol, RedditBase):
+    @property
+    def title(self) -> str: ...
+
+
+def _merge_comments(*sources: Iterator[Comment]) -> Iterator[Comment]:
+    #from .rexport import logger
+    #ignored = 0
+    emitted: Set[str] = set()
+    for e in chain(*sources):
+        uid = e.id
+        if uid in emitted:
+            #ignored += 1
+            #logger.info('ignoring %s: %s', uid, e)
+            continue
+        yield e
+        emitted.add(uid)
+    #logger.info(f"Ignored {ignored} comments...")
+