Game of Greed 2

Understanding Scope

• In programming, the scope of a name defines the area of a program in which you can unambiguously access that name, such as variables, functions, objects, and so on. A name will only be visible to and accessible by the code in its scope. Several programming languages take advantage of scope for avoiding name collisions and unpredictable behaviors. Most commonly, you’ll distinguish two general scopes:

1. Global scope: The names that you define in this scope are available to all your code.

2. Local scope: The names that you define in this scope are only available or visible to the code within the scope.

Using the LEGB Rule for Python Scope

1. Local (or function) scope is the code block or body of any Python function or lambda expression. This Python scope contains the names that you define inside the function. These names will only be visible from the code of the function. It’s created at function call, not at function definition, so you’ll have as many different local scopes as function calls. This is true even if you call the same function multiple times, or recursively. Each call will result in a new local scope being created.

2. Enclosing (or nonlocal) scope is a special scope that only exists for nested functions. If the local scope is an inner or nested function, then the enclosing scope is the scope of the outer or enclosing function. This scope contains the names that you define in the enclosing function. The names in the enclosing scope are visible from the code of the inner and enclosing functions.

3. Global (or module) scope is the top-most scope in a Python program, script, or module. This Python scope contains all of the names that you define at the top level of a program or a module. Names in this Python scope are visible from everywhere in your code.

4. Built-in scope is a special Python scope that’s created or loaded whenever you run a script or open an interactive session. This scope contains names such as keywords, functions, exceptions, and other attributes that are built into Python. Names in this Python scope are also available from everywhere in your code. It’s automatically loaded by Python when you run a program or script.

Conclusion

The scope of a variable or name defines its visibility throughout your code. In Python, scope is implemented as either a Local, Enclosing, Global, or Built-in scope. When you use a variable or name, Python searches these scopes sequentially to resolve it. If the name isn’t found, then you’ll get an error. This is the general mechanism that Python uses for name resolution and is known as the LEGB rule.

You’re now able to:

• Take advantage of Python scope to avoid or minimize bugs related to name collision

• Make good use of global and local names across your programs to improve code maintainability

• Use a coherent strategy to access, modify, or update names across all your Python code

Additionally, you’ve covered some scope-related tools and techniques that Python offers and how you can use them to gather information about the names that live in a given scope or to modify the standard behavior of Python scope. Of course, there’s more to this topic that’s outside the scope of this tutorial, so get out there and continue to tackle name resolution in Python!