+-------+---------------------------------------+
| id | similar |
+-------+---------------------------------------+
| 1 | {3: 1, 2: 2} |
+-------+---------------------------------------+
| 2 | {3: 1, 1: 2} |
+-------+---------------------------------------+
| 3 | {2: 1, 1: 2} |
+-------+---------------------------------------+
+-------+---------------------------------------+
| id | similar_from |
+-------+---------------------------------------+
| 1 | {2: 2, 3: 2} |
+-------+---------------------------------------+
| 2 | {1: 2, 3: 1} |
+-------+---------------------------------------+
| 3 | {1: 1, 3: 1} |
+-------+---------------------------------------+
+-------+---------------------------------------+
| id | similar_from.1 |
+-------+---------------------------------------+
| 1 | null (или 0, не проверял) |
+-------+---------------------------------------+
| 2 | 2 |
+-------+---------------------------------------+
| 3 | 1 |
+-------+---------------------------------------+
if random() > 0.999:
raise SomeCrashError()
С главной страницы библиотеки на гитхабе.