local Statements

Understanding local Statements#

In Python, a variable is only available from inside the region it is created, known as its “scope”. A local variable is one defined within a function and is not accessible outside that function. It exists only within the scope of the function. Here’s a simple example.

1def my_function():
2  local_var = "Hello, World!"
3  print(local_var)
4
5my_function()
6# Outputs: Hello, World!
7
8print(local_var)
9# Error: NameError: name 'local_var' is not defined

In the preceding code snippet, local_var is a local variable of the my_function. You can access local_var within my_function, but once the function execution ends, local_var is destroyed.

If you try to access local_var after the function call, Python throws a NameError because local_var is not defined outside the function scope.

Python’s Scope Resolution#

Here’s one thing you need to bear in mind: Python works on a LEGB rule when it comes to variable scope. This LEGB stands for:

1. Local: Variables defined inside a function or class method. Python checks these first.
2. Enclosing: Variables in the local scope of any and all enclosing functions from inner to outer.
3. Global: Variables declared in the main body of the python code.
4. Built-in: Pre-defined in Python (like open, range, syntax errors).

So, Python will first check if the variable is a Local one, if not it checks for enclosing variables, then global, and finally the built-in ones.

Global vs Local Variables in Python#

To better illustrate the contrast between local and global scopes, let’s modify my_function to include a global variable:

 1global_var = "Hello"
 2
 3def my_function():
 4  local_var = "World!"
 5  print(global_var, local_var)
 6
 7my_function()
 8# Outputs: Hello, World!
 9
10print(global_var)
11# Outputs: Hello
12
13print(local_var)
14# Error: NameError: name 'local_var' is not defined

Here, global_var is defined outside any function, making it a global variable. Inside my_function, we are able to access global_var as well as our local_var. This because global_var exists in the global scope – it’s available everywhere in our code.

Conversely, local_var cannot be accessed outside the function as it only existed during the execution of my_function.

Understanding the differences between local and global scopes can help you manage and manipulate variable access more effectively in function-heavy Python scripts.