python - Python中list类的__contains__方法是如何实现的？

Question

假设我定义了以下变量:

mode = "access"
allowed_modes = ["access", "read", "write"]

我目前有一个类型检查语句是

assert any(mode == allowed_mode for allowed_mode in allowed_modes)

但是，似乎我可以简单地将其替换为

assert mode in allowed_modes

根据 ThiefMaster在 Python List Class __contains__ Method Functionality 中的回答，这两个应该是等价的。真的是这样吗？我如何通过查找 Python 的源代码轻松验证这一点？

Answer 1

不，它们不等同。例如:

>>> mode = float('nan')
>>> allowed_modes = [mode]
>>> any(mode == allowed_mode for allowed_mode in allowed_modes)
False
>>> mode in allowed_modes
True

参见 Membership test operations有关更多详细信息，包括此声明:

For container types such as list, tuple, set, frozenset, dict, or collections.deque, the expression x in y is equivalent to any(x is e or x == e for e in y).