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#4617: Previously it was illegal to delete a name from the local

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namespace if it occurs as a free variable in a nested block.  This limitation
of the compiler has been lifted, and a new opcode introduced (DELETE_DEREF).

This sample was valid in 2.6, but fails to compile in 3.x without this change::

   >>> def f():
   ...     def print_error():
   ...        print(e)
   ...     try:
   ...        something
   ...     except Exception as e:
   ...        print_error()
   ...        # implicit "del e" here


This sample has always been invalid in Python, and now works::

   >>> def outer(x):
   ...     def inner():
   ...        return x
   ...     inner()
   ...     del x

There is no need to bump the PYC magic number: the new opcode is used
for code that did not compile before.
This commit is contained in:
Amaury Forgeot d'Arc 2010-09-10 21:39:53 +00:00
parent 4785916d62
commit ba117ef7e9
12 changed files with 113 additions and 45 deletions
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10
Python/compile.c
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@ -857,6 +857,8 @@ opcode_stack_effect(int opcode, int oparg)
return 1;
case STORE_DEREF:
return -1;
case DELETE_DEREF:
return 0;
default:
fprintf(stderr, "opcode = %d\n", opcode);
Py_FatalError("opcode_stack_effect()");
@ -2506,13 +2508,7 @@ compiler_nameop(struct compiler *c, identifier name, expr_context_ty ctx)
case AugLoad:
case AugStore:
break;
case Del:
PyErr_Format(PyExc_SyntaxError,
"can not delete variable '%S' referenced "
"in nested scope",
name);
Py_DECREF(mangled);
return 0;
case Del: op = DELETE_DEREF; break;
case Param:
default:
PyErr_SetString(PyExc_SystemError,