In Python, what happens when you attempt to access a variable that doesn't exist?

When you attempt to access a variable that doesn't exist in Python, an exception is raised. Specifically, Python throws a NameError, indicating that the variable has not been defined in the local or global scope. This behavior is a fundamental aspect of Python's error handling, designed to alert the programmer to potential issues in the code. When a NameError occurs, the program execution is halted at that point, and you'll see an error message that specifies which variable is undefined.

Understanding this behavior is crucial for debugging and developing robust programs. It prompts you to check for typos, ensure variables are initialized correctly, and confirm that scopes are managed appropriately. This approach discourages silent failures and promotes clarity and explicitness in the code.