exec('var = 1') executed on thread fails to define var

[bperun]

Bug report

Bug description:

import time
import threading

class TestClass(threading.Thread):
    
    def __init__(self):
        threading.Thread.__init__(self)
        self.abort = threading.Event()
    
    def run(self):
        exec('var = 1')
        print(var)
        while True:
            if self.abort.is_set():
                self.abort.clear()
                break
            time.sleep(0.5)

obj = TestClass()
obj.start()
obj.abort.set()

bug.py

Above script also attached for convenience. Produces output:

NameError: name 'var' is not defined. Did you mean: 'vars'?

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[aisk]

This is not a bug related to threading, it has the same behavior without a thread.

And it's not a bug either, inside a function, exec can't create local variables unless you pass it an explicit namespace. See the documentation of exec and locals for details.

I'm closing this issue. If you think the documentation is not clear enough and have ideas on how to improve it, feel free to comment and I'll reopen this as a documentation issue.

[bperun]

This is not a bug related to threading, it has the same behavior without a thread.

And it's not a bug either, inside a function, exec can't create local variables unless you pass it an explicit namespace. See the documentation of exec and locals for details.

I'm closing this issue. If you think the documentation is not clear enough and have ideas on how to improve it, feel free to comment and I'll reopen this as a documentation issue.

When I execute this code without a thread, there is no issue:
exec('var = 1')
print(var)

The documentation doesn't explicitly say (unless I'm missing something) that variables cannot be created if the optional arguments are omitted "In all cases, if the optional parts are omitted, the code is executed in the current scope.".

[aisk]

As I said above, this only happens inside a function:

❯ cat .\a.py
def f():
    exec('var = 1')
    print(var)
f()

~ via 🐍 v3.14.2
❯ python .\a.py
Traceback (most recent call last):
  File "C:\Users\aaaaa\a.py", line 4, in <module>
    f()
    ~^^
  File "C:\Users\aaaaa\a.py", line 3, in f
    print(var)
          ^^^
NameError: name 'var' is not defined. Did you mean: 'vars'?

There is a note in the exec's document:

The default locals act as described for function locals() below. Pass an explicit locals dictionary if you need to see effects of the code on locals after function exec() returns.