Expression of type "Expr | int" cannot be assigned to declared type "Expr"

[sdykae]

I known this is not a problem but for type safe writting, is there a way to craft an Expr that handles the input types and make mypy no mistake?

[oscarbenjamin]

I think the problem is that Expr.__pow__ is actually not type consistent because it sometimes returns unsympified ints. This seems to fix it:

diff --git a/sympy/core/expr.py b/sympy/core/expr.py
index 9fc041f..9a0c299 100644
--- a/sympy/core/expr.py
+++ b/sympy/core/expr.py
@@ -229,10 +229,10 @@ def __pow__(self, other, mod=None):
         try:
             _self, other, mod = as_int(self), as_int(other), as_int(mod)
             if other >= 0:
-                return pow(_self, other, mod)
+                return _sympify(pow(_self, other, mod))
             else:
                 from .numbers import mod_inverse
-                return mod_inverse(pow(_self, -other, mod), mod)
+                return _sympify(mod_inverse(pow(_self, -other, mod), mod))
         except ValueError:
             power = self._pow(other)
             try:

Looks like mod_inverse is also inconsistent.

[nishant-sg]

Hello, I would like to contribute to this issue, can you guide me on what needs to be done?

[fauzank339]

Hello. I want to look into this issue can anyone guide me.

[eagleoflqj]

Now the error is gone, but deduced type becomes Unknown:

from typing_extensions import reveal_type
from sympy import *

x = Symbol('x')
reveal_type(x**2)
reveal_type(x**2-16)

$ pyright test.py
...
  test.py:5:13 - information: Type of "x ** 2" is "Expr"
  test.py:6:13 - information: Type of "x ** 2 - 16" is "Unknown"

Some more type hints should be added so that you don't need to explicitly say fb is Expr.

[eagleoflqj]

No, adding type hints doesn't help due to https://github.com/sympy/sympy/blob/a6e74d2b8b3b64e8cdbf4c2f21835e234eb92d65/sympy/core/expr.py#L204 With the decorator, __sub__ of Expr is a _SympifyWrapper object instead of a method. It's converted back to a method at https://github.com/sympy/sympy/blob/a6e74d2b8b3b64e8cdbf4c2f21835e234eb92d65/sympy/core/decorators.py#L178-L181 It's definitely not understandable by pyright.

[u7122029]

Now the error is gone, but deduced type becomes Unknown:

from typing_extensions import reveal_type
from sympy import *

x = Symbol('x')
reveal_type(x**2)
reveal_type(x**2-16)

$ pyright test.py
...
  test.py:5:13 - information: Type of "x ** 2" is "Expr"
  test.py:6:13 - information: Type of "x ** 2 - 16" is "Unknown"

Some more type hints should be added so that you don't need to explicitly say fb is Expr.

Hey, I just ran your shell test

$ python
...
>>> from typing_extensions import reveal_type
>>> from sympy import *
>>> x = Symbol('x')
>>> reveal_type(x**2)
Runtime type is 'Pow'
x**2
>>> reveal_type(x**2-16)
Runtime type is 'Add'
x**2 - 16

It seems that the expression is being read correctly? Please note that I am a new contributor and I'm not sure how much has changed about sympy since the last comment in this issue. Perhaps I'm wrong to say that we could close this issue.

[eagleoflqj]

No. Please use pyright to test this issue.