Closed
Description
Bug Report
If you reassign a variable with a different (probably compatible) type, mypy still treats it as if it did not change the type
To Reproduce
Analyze this:
from typing import Tuple
class C:
def __init__(self, x, y):
self.x = x
self.y = y
@classmethod
def other_ctor(cls, x, y):
return cls(x, y)
def will_fail(arg: Tuple[int, int]):
arg = C.other_ctor(*arg)
print(arg.x + arg.y)Expected Behavior
Success: no issues found in 1 source file
Actual Behavior
>mypy break_mypy\failure.py
break_mypy\failure.py:16: error: "Tuple[int, int]" has no attribute "x"
break_mypy\failure.py:16: error: "Tuple[int, int]" has no attribute "y"
Found 2 errors in 1 file (checked 1 source file)
Your Environment
- Mypy version used: 0.790
- Mypy command-line flags: none
- Mypy configuration options from
mypy.ini(and other config files): default, freshly installed - Python version used: python 3.6.6 @ Win10 v1909, python 3.7.9 @ Ubuntu 16.04
Additional info
This version without classmethod constructor gives yet another error:
from typing import Tuple
class C:
def __init__(self, x, y):
self.x = x
self.y = y
def will_fail(arg: Tuple[int, int]):
arg = C(*arg)
print(arg.x + arg.y)break_mypy\failure.py:11: error: Incompatible types in assignment (expression has type "C", variable has type "Tuple[int, int]")
break_mypy\failure.py:12: error: "Tuple[int, int]" has no attribute "x"
break_mypy\failure.py:12: error: "Tuple[int, int]" has no attribute "y"
Found 3 errors in 1 file (checked 1 source file)
C was originally a wrapper subclass of namedtuple, but I removed it while working on the MVE.
One more example with namedtuple:
from collections import namedtuple
from typing import Tuple
class C(namedtuple('CNt', 'x y')):
@classmethod
def other_ctor(cls, x, y):
return cls(x, y)
def will_not_fail(arg: Tuple[int, int]):
arg = C(*arg)
print(arg.x + arg.y)
def will_fail(arg: Tuple[int, int]):
arg = C.other_ctor(*arg)
print(arg.x + arg.y)break_mypy\failure.py:18: error: "Tuple[int, int]" has no attribute "x"
break_mypy\failure.py:18: error: "Tuple[int, int]" has no attribute "y"
Found 2 errors in 1 file (checked 1 source file)