Nested Scope Details

With the addition of nested function scopes, variable lookup rules become slightly more complex. Within a function:

 

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  • A reference (X) looks for the name X first in the current local scope (function); then in the local scopes of any lexically enclosing functions in your source code, from inner to outer; then in the current global scope (the module file); and finally in the built-in scope (the module builtins). global declarations make the search begin in the global (module file) scope instead.
  • An assignment (X = value) creates or changes the name X in the current local scope, by default. If X is declared global within the function, the assignment creates or changes the name X in the enclosing module’s scope instead. If, on the other hand, X is declared nonlocal within the function, the assignment changes the name X in the closest enclosing function’s local scope.

Notice that the global declaration still maps variables to the enclosing module. When nested functions are present, variables in enclosing functions may be referenced, but they require nonlocal declarations to be changed.