+---------+----------+--------+
| order_id| customer | amount |
+---------+----------+--------+
|    101  |    C1    |  250   |
|    102  |    C2    |  300   |
|    103  |    C3    |  150   |

+----------+-----------+
| customer | city      |
+----------+-----------+
|   C1     |  Seattle  |
|   C3     |  Boston   |
|   C4     |  Austin   |

Performing a left join in pure Python without external libraries.

Write Python code (no third-party packages) to left-join two lists of dictionaries on key "customer"; discuss an O(N+M) hashing solution.

Contrast nested loops with dict-based look-ups; handle missing matches gracefully.

Citadel Data Scientist interview question: Implement Left Join Using Python Dictionaries Efficiently. {"blocks": [{"key": "e0227ebb", "text": "Orders", "type": "unstyled", "depth": 0, "inlineStyleRanges": [], "entityRanges": [], "data": {}}, ...