Mypy not reporting "undefined" variable.

[neimad1985]

Bug Report

When using a "undefined" variable, which will immediately crash the code when running it, mypy does not report anything about it. Is it normal ?

I feel like mypy should report it but maybe I am wrong because this isn't a typing error. On the other hand, this error is only possible because typing annotations exist . What do you think ?

To Reproduce

Dump this in a file main.py:

number: int
print(number)

Gist URL: https://gist.github.com/mypy-play/31d3775229a6fe01af6bbb09b9230a18
Playground URL: https://mypy-play.net/?mypy=latest&python=3.11&gist=31d3775229a6fe01af6bbb09b9230a18

Expected Behavior

An error message, maybe something like this.

main.py:2: error: Using an undefined variable, a value must be set before first.  [var-undefined]

Actual Behavior

$ mypy --strict main.py
Success: no issues found in 1 source file

python main.py
Traceback (most recent call last):
  File "/home/user/main.py", line 2, in <module>
    print(number)
          ^^^^^^
NameError: name 'number' is not defined

Your Environment

• Mypy version used: 1.3.0
• Mypy command-line flags: --strict
• Mypy configuration options from mypy.ini (and other config files): nothing
• Python version used: 3.11.3

[ikonst]

From mypy's perspective, "uninitialized" or "unassigned" probably described it better than "undefined". Maybe change the title to "Not reporting uninitialized variable read"?

This seems related to #4019 but not quite the same (at first glance, #4019 seems much more complicated, since a declared class attribute might or might not be initialized elsewhere).