eval() cannot see local variables in a method (or those passed in as function parameters)

[ericzundel]

CircuitPython version and board name

Adafruit CircuitPython 10.0.1 on 2025-10-09; Adafruit Feather nRF52840 Express with nRF52840

Code/REPL

def eval_test(foo):
    global loops
    bar=1
    eval("print('Hello')")
    eval('print(f"loops is {loops}")')

    # passing a dict for the locals parameter works:
    eval('print(f"foo is {foo} bar is {bar}")', 
         {}, {"foo":foo, "bar": bar}) 

    # Fails with: NameError: name 'bar' isn't defined
    #eval('print(f"bar is {bar}")') 
    
    # Fails with: NameError: name 'foo' isn't defined
    #eval('print(f"foo is {foo}")') 

loops=1
eval_test(9)

Behavior

When referencing a name in the local scope, you get: NameError: name 'foo' isn't defined

But you can create and pass a local scope and it works.

Description

No response

Additional information

I looked around and didn't see that this was a known issue.

[todbot]

I believe this is a micropython limitation rather than specifically a CircuitPython issue.

% micropython
MicroPython v1.26.1 on 2025-09-11; darwin [Clang 17.0.0] version
Use Ctrl-D to exit, Ctrl-E for paste mode
>>> 
paste mode; Ctrl-C to cancel, Ctrl-D to finish
=== def eval_test(foo):
===     global loops
===     bar=1
===     print("foo",foo)
===     eval('print(f"loops is {loops}")')
===     eval('print(f"foo is {foo}")') 
=== 
=== loops=1
=== eval_test(9)
=== 
foo 9
loops is 1
Traceback (most recent call last):
  File "<stdin>", line 9, in <module>
  File "<stdin>", line 6, in eval_test
  File "<string>", line 1, in <module>
NameError: name 'foo' isn't defined

[ericzundel]

Found this: https://docs.micropython.org/en/latest/genrst/core_language.html#code-running-in-eval-function-doesn-t-have-access-to-local-variables
and an issue someone filed: micropython#15883

They left the issue open, but it doesn't sound like something that they will want to fix.