Python closure & late binding 陷阱
不囉嗦直接看code
```python=
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class TC:
def __init__(self,
condition_list: list = ['A']):
self.condition_list = condition_list
def add(self):
temp_tc = TC()
self.condition_list.extend(temp_tc.condition_list)
tc1 = TC() tc1.add() print(tc1.condition_list) tc2 = TC() tc2.add() print(tc2.condition_list) tc3 = TC() tc3.add() print(tc3.condition_list)
## 很直覺的答案應該是如下
```bash=
['A', 'A']
['A', 'A']
['A', 'A']
但是結果卻是如下
bash=
['A', 'A']
['A', 'A', 'A', 'A']
['A', 'A', 'A', 'A', 'A', 'A', 'A', 'A']
結論
很明顯這有很嚴重的 memory leak 的 issue 主要是closure讓區域變數無法release, condition_list 看似已經從內存中消失了，但依然能夠訪問到 condition_list 這個非局部變量！