I created a class with a list attribute containing an int and a float. I then tried creating a getter method to return the list as a tuple.
from typing import Tuple, List
class MyClass:
def __init__(self):
self.__lst = [3, 5.0]
def get_lst_as_tup(self) -> Tuple[int, float]:
return tuple(self.__lst)
while it seems to work properly, PyCharm presents a problem:
Expected type 'Tuple[int, float]', got 'Tuple[Union[int, float], ...]' instead
after seeking stack overflow I tried several other implementations for the return statement. that resulted in the same error:
return (element for element in self.__lst)
return tuple(element for element in self.__lst)
return (*self.__lst,) this specific implementation resulted in :
Expected type 'Tuple[int, float]', got 'Tuple[Any]' instead
I was able to get rid of the error by using return self.__lst[0], self.__lst[1]
but I do not understand why it does not accept the other implementations.
Notes: I did not use the word tuple elsewhere in the file. This error occures even when this is all there is in the file.
For your example
return (element for element in self.__lst)
I doubt that you got the same error as this in fact returns a generator and not a tuple.
Your other attempts
return tuple(self.__lst)
return (*self.__lst,)
return tuple(element for element in self.__lst)
are all valid approaches to convert the list self.__lst into a tuple. Of course, the most readable is tuple(self.__lst), so you should probably stick with this.
I think the suggested type Tuple[Union[int, float], ...] is still too narrow here. You are converting a list which is of variable length into a tuple. There is no way of knowing which length self.__lst will have in your program. Consider this:
m = MyClass()
m._MyClass__lst.append("hello")
r = m.get_lst_as_tup()
print(r)
Output:
(3, 5.0, 'hello')
Which is of type Tuple[int, float, str].
However, when you use return self.__lst[0], self.__lst[1] it is guaranteed that the function will return a tuple of length 2 (or throw an exception if the list became smaller than length 2).