What is variable scope in Python and how does the LEGB rule work?

Scope determines where in the code a variable name is visible and accessible. Python resolves names using the LEGB rule, checking four scopes in order: Local → Enclosing → Global → Built-in.

x = 'global'

def outer():
    x = 'enclosing'

    def inner():
        x = 'local'
        print(x)  # local

    inner()
    print(x)      # enclosing

outer()
print(x)          # global

L – Local: names assigned inside the current function.
E – Enclosing: names in any enclosing (outer) function's scope — relevant for nested functions and closures.
G – Global: names assigned at the module's top level.
B – Built-in: names built into Python itself — len, print, range, etc.

To assign to a global variable from inside a function, declare it with global name. To assign to an enclosing-scope variable, use nonlocal name (Python 3+). Without these declarations, Python creates a new local variable instead of modifying the outer one, which is a very common source of bugs in interviews.

count = 0

def increment():
    global count
    count += 1

increment()
print(count)  # 1

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