What is the LEGB rule for scope resolution? | Interview Question

Q: What is the LEGB rule for scope resolution?

**Target Audience:** Python beginners and intermediate developers preparing for interviews — you only need to know what a function is. **Difficulty:** Medium **Python version:** Behaviour checked on CPython 3.11, 3.12 and 3.13; the examples run in the page on Pyodide 0.25.1 (CPython 3.11.3). > **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. Every output shown was produced by actually running the code — see the **Verified** section. ## 1. Why This Even Matters — A Story First You walk into a big office block and shout "Sam!". First the people in your own room look up — if there is a Sam in the room, that is the Sam you meant. If not, the people on your floor answer. If there is no Sam on your floor either, the whole building is asked, and as a last resort you check the city phone book of well-known Sams. You stop at the **first** Sam you find, even if a "better" Sa

The problem

Question presented to candidate: "When Python meets a name like total inside a function, how does it decide which variable you mean? Walk me through the LEGB rule and the cases where it surprises people."

What a strong answer should cover:

The search order Local, Enclosing function, Global (module), Built-in; the first match wins and a miss raises NameError.
Scope is decided at compile time: an assignment anywhere in a function makes the name local for the whole body, which is why reading it first raises UnboundLocalError.
Only modules, functions, lambdas, comprehensions and class bodies create scopes; if, for, with and try blocks do not.
Class bodies are skipped: a method cannot see class attributes as bare names, it must use self.x or ClassName.x.
Reading follows LEGB, but rebinding an outer name needs global or nonlocal; shadowing a built-in such as list or len hides it.
A CPython detail: the compiler emits LOAD_FAST, LOAD_DEREF or LOAD_GLOBAL, and LOAD_GLOBAL checks the module dict first and the builtins second.

Code / implementation expected: Optional — predict the output of a nested-function snippet, or explain the UnboundLocalError case.

scope
legb

Try it yourself

Sketch your approach before you read the solution. That is what the interview tests.

Stuck? Get a hint.

A short nudge toward the approach. It will not give the answer away.

Solution

Target Audience: Python beginners and intermediate developers preparing for interviews — you only need to know what a function is. Difficulty: Medium Python version: Behaviour checked on CPython 3.11, 3.12 and 3.13; the examples run in the page on Pyodide 0.25.1 (CPython 3.11.3).

How to read this doc: Each idea is explained in plain language first, then tagged with 📌 Interview term: so you also learn the exact word an interviewer expects. Every output shown was produced by actually running the code — see the Verified section.

1. Why This Even Matters — A Story First

You walk into a big office block and shout "Sam!". First the people in your own room look up — if there is a Sam in the room, that is the Sam you meant. If not, the people on your floor answer. If there is no Sam on your floor either, the whole building is asked, and as a last resort you check t

The solution is hidden so you can try first

12 min read · 12 sections

Run the code

Edit the code and run it here. Each console line with an expected value becomes a test.

PythonLEGB in action: the four scopes, shadowing, and what is not a scope

Practice

PythonCompile time decides: UnboundLocalError, dis, symtable and class bodies

Practice

Discussion

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