bpo-34983: Expose symtable.Symbol.is_nonlocal() in the symtable module (GH-9872)

The symbol table was not exposing functionality to query the nonlocal symbols in a function or to check if a particular symbol is nonlocal.

Author: pablogsal

Doc/library/symtable.rst

@@ -105,6 +105,10 @@ Examining Symbol Tables
 
  Return a tuple containing names of globals in this function.
 
+ .. method:: get_nonlocals()
+
+ Return a tuple containing names of nonlocals in this function.
+
  .. method:: get_frees()
 
  Return a tuple containing names of free variables in this function.
@@ -144,6 +148,10 @@ Examining Symbol Tables
 
  Return ``True`` if the symbol is global.
 
+ .. method:: is_nonlocal()
+
+ Return ``True`` if the symbol is nonlocal.
+
  .. method:: is_declared_global()
 
  Return ``True`` if the symbol is declared global with a global statement.

Lib/symtable.py

@@ -1,7 +1,7 @@
 """Interface to the compiler's internal symbol tables"""
 
 import _symtable
-from _symtable import (USE, DEF_GLOBAL, DEF_LOCAL, DEF_PARAM,
+from _symtable import (USE, DEF_GLOBAL, DEF_NONLOCAL, DEF_LOCAL, DEF_PARAM,
  DEF_IMPORT, DEF_BOUND, DEF_ANNOT, SCOPE_OFF, SCOPE_MASK, FREE,
  LOCAL, GLOBAL_IMPLICIT, GLOBAL_EXPLICIT, CELL)
 
@@ -117,6 +117,7 @@ class Function(SymbolTable):
  __locals = None
  __frees = None
  __globals = None
+ __nonlocals = None
 
  def __idents_matching(self, test_func):
  return tuple(ident for ident in self.get_identifiers()
@@ -141,6 +142,11 @@ def get_globals(self):
  self.__globals = self.__idents_matching(test)
  return self.__globals
 
+ def get_nonlocals(self):
+ if self.__nonlocals is None:
+ self.__nonlocals = self.__idents_matching(lambda x:x & DEF_NONLOCAL)
+ return self.__nonlocals
+
  def get_frees(self):
  if self.__frees is None:
  is_free = lambda x:((x >> SCOPE_OFF) & SCOPE_MASK) == FREE
@@ -184,6 +190,9 @@ def is_parameter(self):
  def is_global(self):
  return bool(self.__scope in (GLOBAL_IMPLICIT, GLOBAL_EXPLICIT))
 
+ def is_nonlocal(self):
+ return bool(self.__flags & DEF_NONLOCAL)
+
  def is_declared_global(self):
  return bool(self.__scope == GLOBAL_EXPLICIT)
 

Lib/test/test_symtable.py

@@ -10,6 +10,7 @@
 import sys
 
 glob = 42
+some_var = 12
 
 class Mine:
  instance_var = 24
@@ -19,10 +20,15 @@ def a_method(p1, p2):
 def spam(a, b, *var, **kw):
  global bar
  bar = 47
+ some_var = 10
  x = 23
  glob
  def internal():
  return x
+ def other_internal():
+ nonlocal some_var
+ some_var = 3
+ return some_var
  return internal
 
 def foo():
@@ -47,6 +53,7 @@ class SymtableTest(unittest.TestCase):
  a_method = find_block(Mine, "a_method")
  spam = find_block(top, "spam")
  internal = find_block(spam, "internal")
+ other_internal = find_block(spam, "other_internal")
  foo = find_block(top, "foo")
 
  def test_type(self):
@@ -75,12 +82,12 @@ def test_children(self):
 
  def test_lineno(self):
  self.assertEqual(self.top.get_lineno(), 0)
- self.assertEqual(self.spam.get_lineno(), 11)
+ self.assertEqual(self.spam.get_lineno(), 12)
 
  def test_function_info(self):
  func = self.spam
  self.assertEqual(sorted(func.get_parameters()), ["a", "b", "kw", "var"])
- expected = ["a", "b", "internal", "kw", "var", "x"]
+ expected = ['a', 'b', 'internal', 'kw', 'other_internal', 'some_var', 'var', 'x']
  self.assertEqual(sorted(func.get_locals()), expected)
  self.assertEqual(sorted(func.get_globals()), ["bar", "glob"])
  self.assertEqual(self.internal.get_frees(), ("x",))
@@ -93,6 +100,12 @@ def test_globals(self):
  self.assertFalse(self.internal.lookup("x").is_global())
  self.assertFalse(self.Mine.lookup("instance_var").is_global())
 
+ def test_nonlocal(self):
+ self.assertFalse(self.spam.lookup("some_var").is_nonlocal())
+ self.assertTrue(self.other_internal.lookup("some_var").is_nonlocal())
+ expected = ("some_var",)
+ self.assertEqual(self.other_internal.get_nonlocals(), expected)
+
  def test_local(self):
  self.assertTrue(self.spam.lookup("x").is_local())
  self.assertFalse(self.internal.lookup("x").is_local())

Misc/NEWS.d/next/Core and Builtins/2018-10-14-17-26-41.bpo-34983.l8XaZd.rst

@@ -0,0 +1,2 @@
+Expose :meth:`symtable.Symbol.is_nonlocal` in the symtable module. Patch by
+Pablo Galindo.

Modules/symtablemodule.c

@@ -84,6 +84,7 @@ PyInit__symtable(void)
  return NULL;
  PyModule_AddIntMacro(m, USE);
  PyModule_AddIntMacro(m, DEF_GLOBAL);
+ PyModule_AddIntMacro(m, DEF_NONLOCAL);
  PyModule_AddIntMacro(m, DEF_LOCAL);
  PyModule_AddIntMacro(m, DEF_PARAM);
  PyModule_AddIntMacro(m, DEF_FREE);