Description
Bug Report
When creating lists or tuples of a fixed (initial) length using multiplication with a constant (i.e. 3*[1]) mypy evaluates the type as "Tuple[XXX, ...]", even though the length of the list/tuple is known.
This leads to incompatibilities when assigning values to existing variables that were constructed "classically" (i.e. [1, 1, 1]).
I don't know if this is intentional or actually a bug.
If the type will be changed to "Tuple[XXX, XXX, XXX]" this could lead to long expressions for long lists (i.e. 1e4*[1]).
Is it possible to remove the incompatibility or will this lead to other inconsistencies?
To Reproduce
Here is a minimal example on how to reproduce the problem:
var = (1, 2, 3)
var = 3 * (1,)
I know, that this is quite useless code, but a more often encountered code example with the same problem would be:
if cond:
var = (1, 2, 3)
else:
var = 3 * (1,)
Expected Behavior
Both expressions should evaluate to Tuple[int, int, int] OR be compatible.
Actual Behavior
This raises:
Incompatible types in assignment (expression has type "Tuple[int, ...]", variable has type "Tuple[int, int, int]")
Your Environment
- Mypy version used: 0.812
- Mypy command-line flags: /
- Mypy configuration options from
mypy.ini(and other config files): / - Python version used: 3.9.1
- Operating system and version: redhat enterprise linux 7
Comment
I have no idea what the operation 5*(1,) is called, so I could not find anything about this problem. Sorry, if this was asked/resolved before.