The nonlocal Statement

In the prior section we explored the way that nested functions can reference variables in an enclosing function’s scope, even if that function has already returned. It turns out that, as of Python 3.0, we can also change such enclosing scope variables, as long as we declare them in nonlocal statements. With this statement, nested defs can have both read and write access to names in enclosing functions.

The nonlocal statement is a close cousin to global, covered earlier. Like global, nonlocal declares that a name will be changed in an enclosing scope. Unlike global, though, nonlocal applies to a name in an enclosing function’s scope, not the global module scope outside all defs. Also unlike global, nonlocal names must already exist in the enclosing function’s scope when declared—they can exist only in enclosing functions and cannot be created by a first assignment in a nested def.

广告：个人专属 VPN，独立 IP，无限流量，多机房切换，还可以屏蔽广告和恶意软件，每月最低仅 5 美元

In other words, nonlocal both allows assignment to names in enclosing function scopes and limits scope lookups for such names to enclosing defs. The net effect is a more direct and reliable implementation of changeable state information, for programs that do not desire or need classes with attributes.