英文:
mypy: Incompatible types in assignment when overwriting a variable
问题
我在运行版本为0.942的mypy时遇到了“assignment”错误，但我无法理解。
我有一个名为price_point的变量，它采用字符串的形式，并根据字符串是否包含“-”来确定在传递给另一个函数_other_func()之前是否将该变量转换为列表。该变量也可以为None。
尝试 1:
代码如下：
def _other_func(price_points: Optional[Union[List[str], str]]) -> float:return 1.0def get_rate(price_point: Optional[str]) -> float:"""Args:price_point: 表示单个价格或价格范围的字符串，例如 '100' 或 '100-200'。也可以为None。"""if price_point and len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")price_point = price_point_rangereturn _other_func(price_point)
错误信息：
error: Incompatible types in assignment (expression has type "List[str]", variable has type "Optional[str]") [assignment]price_point = price_point_range^
有人能解释一下为什么mypy关心这个变量吗？因为_other_func()输入类型的联合中包含了List类型。我愿意听取其他建议。
尝试 2:
我认为问题可能与变量的名称有关，因此我尝试了以下方法来将变量重命名，然后将其传递给_other_func()：
def get_rate(price_point: Optional[str]) -> float:"""Args:price_point: 表示单个价格或价格范围的字符串，例如 '100' 或 '100-200'。也可以为None。"""if price_point and len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")price_point_input = price_point_rangeelse:price_point_input = price_pointreturn _other_func(price_point_input)
但是相同的错误仍然存在：
error: Incompatible types in assignment (expression has type "Optional[str]", variable has type "List[str]") [assignment]price_point_input = price_point^
我不确定是不是因为盯着屏幕看太久的缘故...
英文:
I'm getting an assignment error when running mypy version 0.942 on my script that I can't make sense of.
I have a variable price_point that takes the form of a string, and depending on if the string contains a "-", will determine if the variable is manipulated into a list before being passed to another function _other_func(). The variable can also be None.
Attempt 1:
The code:
<!-- language: python -->
def _other_func(price_points: Optional[Union[List[str], str]]) -> float:return 1.0def get_rate(price_point: Optional[str])->float:"""Args:price_point: String representing single price or range of pricese.g. '100' or '100-200'. Can also be None."""if price_point and len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")price_point = price_point_rangereturn _other_func(price_point)
<!-- end snippet -->
Error returned:
error: Incompatible types in assignment (expression has type "List[str]", variable has type "Optional[str]") [assignment]price_point = price_point_range^
Can someone please explain why mypy is concerned about this variable, since the List type is accounted for in the Union of types in the _other_func() input? I'd be open to hearing alternate suggetions.
Attempt 2:
I thought the issue might be to do with the name of the variable, so I tried this alternative to rename the variable before passing it to _other_func():
<!-- language: python -->
def get_rate(price_point: Optional[str])->float:"""Args:price_point: String representing single price or range of pricese.g. '100' or '100-200'. Can also be None."""if price_point and len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")price_point_input = price_point_rangeelse:price_point_input = price_pointreturn _other_func(price_point_input)
<!-- end snippet -->
But the same error persists:
error: Incompatible types in assignment (expression has type "Optional[str]", variable has type "List[str]") [assignment]price_point_input = price_point^
I'm not sure if I'm just having one of those days of staring at the screen for too long...
答案1
得分: 2
静态类型在运行时不能改变。price_point 是一个 Optional[str] 类型，必须在调用 get_rate 函数的整个过程中保持不变。如果你想向 other_func 传递不同类型的值，你需要使用一个不同的变量，可以容纳字符串或列表（或 None）：
def get_rate(price_point: Optional[str]) -> float:"""Args:price_point: 表示单个价格或价格范围的字符串，例如 '100' 或 '100-200'，也可以是 None。"""arg: Optional[Union[list[str], str]] = price_pointif price_point and len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")arg = price_point_rangereturn _other_func(arg)
然而，我可能会跳过新变量，只是调用 _other_func 两次，每次传递适当的参数：
def get_rate(price_point: Optional[str]) -> float:"""Args:price_point: 表示单个价格或价格范围的字符串，例如 '100' 或 '100-200'，也可以是 None。"""if price_point and len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")return _other_func(price_point_range)return _other_func(price_point)
更好的做法是考虑将这三种可能性统一到单一类型 list[str] 下，该类型应该包含 0、1 或 2 个字符串：
def _other_func(price_points: list[str]) -> float:match len(price_points):case 0:... # 旧的 None 情况case 1:... # 旧的字符串情况case 2:... # 旧的 list[str] 情况case _:raise ValueError("列表中的项目太多")def get_rate(price_point: Optional[str]) -> float:arg: list[str]if not price_point:arg = []elif len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")arg = price_point_rangeelse:arg = [price_point]return _other_func(arg)
英文:
Static types cannot be changed at runtime. price_point is a Optional[str], and it must stay that way for the duration of the call to get_rate. If you want to pass a value of a different type to other_func, you need to use a different variable that can hold either a string or a list (or None):
def get_rate(price_point: Optional[str])->float:"""Args:price_point: String representing single price or range of pricese.g. '100' or '100-200'. Can also be None."""arg: Optional[Union[list[str], str]] = price_pointif price_point and len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")arg = price_point_rangereturn _other_func(arg)
However, I would probably skip the new variable, and just make two calls to _other_func, each with the appropriate argument.
def get_rate(price_point: Optional[str])->float:"""Args:price_point: String representing single price or range of pricese.g. '100' or '100-200'. Can also be None."""if price_point and len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")return _other_func(price_point_range)return _other_func(price_point)
Even better, consider "unifying" the three possibilities under the single type list[str], which should hold 0, 1, or 2 strings.
def _other_func(price_points: list[str]) -> float:match len(price_points):case 0:... # Old None casecase 1:... # Old str casecase 2:... # Old list[str] casecase _:raise ValueError("Too many items in the list")def get_rate(price_point: Optional[str])->float:arg: list[str]if not price_point:arg = []elif len(price_point_range := price_point.split("-")) > 1:print(f"Checking range {price_point_range[0]} to {price_point_range[1]}")arg = price_point_rangeelse:arg = [price_point]return _other_func(arg)
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