Add big news item about nested scopes, __future__, and compile-time

warnings.
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Guido van Rossum 2001-03-02 14:00:32 +00:00
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@ -3,6 +3,42 @@ What's New in Python 2.1 beta 1?
Core language, builtins, and interpreter
- Following an outcry from the community about the amount of code
broken by the nested scopes feature introduced in 2.1a2, we decided
to make this feature optional, and to wait until Python 2.2 (or at
least 6 months) to make it standard. The option can be enabled on a
per-module basis by adding "from __future__ import nested_scopes" at
the beginning of a module (before any other statements, but after
comments and an optional docstring). See PEP 236 (Back to the
__future__) for a description of the __future__ statement. PEP 227
(Statically Nested Scopes) has been updated to reflect this change,
and to clarify the semantics in a number of endcases.
- The nested scopes code, when enabled, has been hardened, and most
bugs and memory leaks in it have been fixed.
- Compile-time warnings are now generated for a number of conditions
that will break or change in meaning when nested scopes are enabled:
- Using "from...import *" or "exec" without in-clause in a function
scope that also defines a lambda or nested function with one or
more free (non-local) variables. The presence of the import* or
bare exec makes it impossible for the compiler to determine the
exact set of local variables in the outer scope, which makes it
impossible to determine the bindings for free variables in the
inner scope. To avoid the warning about import *, change it into
an import of explicitly name object, or move the import* statement
to the global scope; to avoid the warning about bare exec, use
exec...in... (a good idea anyway -- there's a possibility that
bare exec will be deprecated in the future).
- Use of a global variable in a nested scope with the same name as a
local variable in a surrounding scope. This will change in
meaning with nested scopes: the name in the inner scope will
reference the variable in the outer scope rather than the global
of the same name. To avoid the warning, either rename the outer
variable, or use a global statement in the inner function.
- An optional object allocator has been included. This allocator is
optimized for Python objects and should be faster and use less memory
than the standard system allocator. It is not enabled by default