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say, I have very simple piece of code

py = """ a = 1 print (f'before all {a=}') def bar(n): print(f'bye {n=}') def foo(n): print(f'hello {n=}') bar(n) bar ('just works') foo ('sara') """ loc = {} glo = {} bytecode = compile(py, "script", "exec") exec(bytecode, glo, loc)

as you can see I defined two functions: bar & foo and called both of them with results:

before all a=1 bye n='just works' hello n='sara' Traceback (most recent call last): File "/home/bla-bla/pythonProject/main_deco2.py", line 43, in <module> exec(bytecode, glo, loc) File "script", line 13, in <module> File "script", line 10, in foo NameError: name 'bar' is not defined

and this leaves me puzzled, as I don't understand why function foo doesn't see bar when just a second ago I was able to call bar without a problem ?

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    As a lead: if you skip the foo parts in the code, and examine the dicts afterwards, you will find that a and bar end up in the locals dict, not the globals dict. Commented Oct 3, 2022 at 21:07

2 Answers 2

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From the docs:

If exec gets two separate objects as globals and locals, the code will be executed as if it were embedded in a class definition.

That's not what you want, so don't provide a locals.

glo = {} exec(bytecode, glo)

Output, for reference:

before all a=1 bye n='just works' hello n='sara' bye n='sara'
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P.S. I haven't quite wrapped my head around why it's treated as if it were in a class definition, so if anyone could explain it, I'm all ears. I do understand that class scope is kinda weird though, so it's probably related to that.
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An important diagnostic:

>>> dis.dis(bytecode) 2 0 LOAD_CONST 0 (1) 2 STORE_NAME 0 (a) 3 4 LOAD_NAME 1 (print) 6 LOAD_CONST 1 ('before all a=') 8 LOAD_NAME 0 (a) 10 FORMAT_VALUE 2 (repr) 12 BUILD_STRING 2 14 CALL_FUNCTION 1 16 POP_TOP

I omitted most of the result, but the first few lines show what is going on. Accesses to a and bar use the LOAD_NAME and STORE_NAME opcodes, which use the locals first. (It cannot use LOAD_FAST because it is not a compiled function.) To work around this, simply mark the necessary names as global explicitly.

Unfortunately, I don't have a good answer for why it does this.

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