Python Static Class Variable 的行爲

隨手記下今天遇到的 Python Static Class Variable 的行爲：

>>> class Test():
... REQUESTS_PER_SECOND = 1
...


直接訪問：

>>> Test.REQUESTS_PER_SECOND
1


重新賦值，instance 繼承新值：

>>> Test.REQUESTS_PER_SECOND = 2
>>> t = Test()
>>> t.REQUESTS_PER_SECOND
2


再次重新賦值，instance 再次繼承新值：

>>> Test.REQUESTS_PER_SECOND = 3
>>> t.REQUESTS_PER_SECOND
3


instance 賦值，對 static class variable 無影響：

>>> t.REQUESTS_PER_SECOND = 4
>>> Test.REQUESTS_PER_SECOND
3


已賦值過的 instance 不再受 class 的影響：

>>> Test.REQUESTS_PER_SECOND = 5
>>> t.REQUESTS_PER_SECOND
4