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What is the difference between positional arguments and keyword arguments when calling a function? How do default parameter values work, and when are they evaluated? What does it mean that functions are 'first-class objects' in Python? Why do you need the 'global' keyword to MODIFY a global variable from inside a function, but not to simply READ it? How does the 'nonlocal' keyword let a nested function modify a variable in its ENCLOSING (not global) scope? How do *args and **kwargs let a function accept an arbitrary number of positional and keyword arguments? Why is using a mutable default argument (like an empty list) a classic Python bug, and how do you avoid it? How do keyword-only arguments (using a bare '*' in the parameter list) force certain parameters to be passed by name only? How do positional-only parameters (using a bare '/' in the parameter list, Python 3.8+) restrict how certain parameters can be passed? How does a closure capture variables from its enclosing scope, and what pitfall occurs when creating multiple closures inside a loop?
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What is Python's LEGB rule for variable scope resolution, and what does each letter stand for?

Intermediate

Answer

LEGB describes the order Python searches for a variable name: Local (the current function), Enclosing (any outer function, for closures), Global (the module level), and Built-in (Python's built-in names like len or print) — Python looks in each scope in that order and uses the FIRST match found.
x = "global"
def outer():
    x = "enclosing"
    def inner():
        x = "local"
        print(x)  # 'local' -- found in Local scope first
    inner()
outer()
Real-world example Understanding exactly which 'x' a function refers to when the same name exists at multiple scope levels.

Common follow-ups: What happens if a variable name isn't found in ANY of the four LEGB scopes?

OOP
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