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);