library symtable.SymbolTable.is_nested() description differs from Cpython implementation.

Open
#99,350 3 comments 0 reactions 0 assignees View on GitHub

Nobody has claimed this yet.

Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
20/100
Issue type
Documentation
Clarity
Needs clarification
Activity status
Stale
Tech stack
python
Domain
documentation

Research direction

Review linked PR gh-151901 first, then compare the symtable and inspect documentation with the stated CPython behavior and the CO_NESTED flag. The issue leaves the resolution open: either align implementation and add compiler tests, or correct the documentation and possibly deprecate the feature.

Written by the indexing model from the issue text.

Description

docs interpreter-core type-bug

The documentation says

is_nested()
Return True if the block is a nested class or function.

The cpython implementation of symtable.c sets the corresponding flag only if the block is nested somewhere inside a function. This would include, for example, a scope inside a class inside a function.

Thus

def f():    # false
  def g():    # true
    def h():    # true
    class C:    # true
  class B:    # true
    def h():    # true
    class C:    # true
class A:    # false
  def g():    # false !!
    def h():    # true
    class C:    # true
  class B:    # false !!
    def h():    # false !!
    class C:    # false !!

The value is the same as the CO_NESTED bit in the code object's co_flags member.
The flag is also documented (similarly incorrectly) in the inspect module documentation.

I would recommend deprecating this feature. The documentation for co_flags says that

bits 0x10 and 0x1000 were used in earlier versions of Python.

0x10 is the CO_NESTED bit. I would guess that nobody uses CO_NESTED or SymbolTable.is_nested().

Alternatives:

  • Change the behavior in Cpython to agree with the documentation. A class nested in another scope should also have CO_NESTED set. Make a test case for the compiler, to ensure that other implementations follow the same definition.
  • Correct the documentation for symtable and inspect modules. Possibly also deprecate the feature.
Linked PRs
  • gh-151901
Dominant language
Python
Stars
77.2k
Forks
36k
Avg merge
1d 9h
Merged PRs (30d)
558

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

More from python/cpython

All issues in python/cpython

Similar issues

More Python issues

Get new issues in your inbox

A short digest of beginner-friendly GitHub issues.