6.11 Namespaces and scope resolution

Namespace

• A namespace maps names to objects.
• The Python interpreter uses namespaces to track all of the objects in a program

• In fact, a namespace is actually just a normal Python dictionary whose keys are the names and whose values are the objects

  • A programmer can examine the names in the current local and global namespace by using the locals() and globals() built-in functions.

  

Scope and scope resolution

• Scope is the area of code where a name is visible.
• Namespaces are used to make scope work.
• Each scope, such as global scope or a local function scope, has its own namespace
• If a namespace contains a name at a specific location in the code, then that name is visible and a programmer can use it in an expression.

There are at least three nested scopes that are active at any point in a program's execution: 1

1. Built-in scope – Contains all of the built-in names of Python, such as int(), str(), list(), range(), etc.
2. Global scope – Contains all globally defined names outside of any functions.
3. Local scope – Usually refers to scope within the currently executing function, but is the same as global scope if no function is executing.
4. When a name is referenced in code, the local scope's namespace is the first checked, followed by the global scope, and finally the built-in scope.
5. If the name cannot be found in any namespace, the interpreter generates a NameError.
6. The process of searching for a name in the available namespaces is called scope resolution.

More scoping and namespaces

Note that the Python Tutor tool uses the term "frame" in place of "namespace".