Recently I am learning about scoping in Python. I understand what is a stack frame but I am confused about the relation and difference between a stack frame and a scope. I study Python through the book 《Introduction to Computation and Programming Using Python》. It does not specifically clarify these two terms.

CodePudding user response：

Scope is just one of the LEGB: Local, Enclosing, Global and Built-in. They are namespaces that Python uses to look up names. LEGB is the order in which that lookup is performed, first the local scope is checked for a names, then the enclosing scope, then global, built-in and if it's never found, you end up with an exception.

This ordering is the reason for 'shadowing': if you define something in local scope, it shadows global, because local scope is checked before global scope. The definition doesn't overwrite the previous one, it shadows it. If you redefine a variable in the same scope, it overwrites the previous variable and you can't get it back.

A stack frame is created every time a function is called (and a global frame every time a module is loaded). The stack frame handles the local variables for the function. Every time another function is called, a new stack frame is created, creating a new local scope. This allows every call to a function to have its own set of local variables, without access to the local scope of previous calls. Every time a function returns, that stack frame is destroyed, and you end back up in the previous stack frame (so, it's a 'stack').

So 'stack frame' is related to 'scope' in that the local scope is on the top-most stack frame. A stack frame contains the local scope for a function call, and a global frame contains the global scope for a module.