Add simple script to count ancestors.

count_ancestors.py

@@ -0,0 +1,26 @@
+import argparse
+
+import data_reader
+
+
+def count_ancestors(db, start_num, args):
+  last_gen = [start_num]
+  for gen_num in range(1, args.max_gens + 1):
+    next_gen = []
+    for person_num in last_gen:
+      next_gen.extend(db.parents_of(person_num))
+    print(f" * Gen {gen_num:3d} : {len(next_gen):7_d} / {2**gen_num:7_d} ({len(next_gen) /2**gen_num:4.0%}) Growth: {len(next_gen) / len(last_gen):4.2f}x")
+    last_gen = next_gen
+
+
+if __name__ == "__main__":
+  parser = argparse.ArgumentParser()
+  parser.add_argument("wikitree_id")
+  parser.add_argument("--version", help="Data version (defaults to most recent).")
+  parser.add_argument("--max-gens", type=int, default=30)
+  args = parser.parse_args()
+
+  db = data_reader.Database(args.version)
+  start_num = db.id2num(args.wikitree_id)
+
+  count_ancestors(db, start_num, args)