Eryk Sun added the comment:
The class example defines "i" as a local variable, which means the CPython
operation used for unoptimized code (class or module/exec) is LOAD_NAME, which
searches locals, globals, and builtins. The result differs from the exec
example because a class is executed with a new locals dict to capture the class
namespace.
I think a more interesting case to explain is code that uses LOAD_CLASSDEREF.
This operation tries locals and nonlocals, but not globals or builtins.
i = 'global'
def f():
i = 'nonlocal'
class C:
print(i)
>>> f()
nonlocal
i = 'global'
def f():
class C:
print(i)
i = 'nonlocal'
>>> f()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 2, in f
File "<stdin>", line 3, in C
NameError: free variable 'i' referenced before assignment in enclosing scope
i = 'global'
def f():
class C:
locals()['i'] = 'local'
print(i)
i = 'nonlocal'
>>> f()
local
i = 'global'
def f():
i = 'nonlocal'
class C:
nonlocal i
print(i)
i = 'new nonlocal'
print(i)
print(i)
>>> f()
nonlocal
new nonlocal
new nonlocal
----------
nosy: +eryksun
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