Closures and Decorators Flashcards

What is a closure in Python?

Answer: An inner function that captures and remembers variables from the enclosing scope even after the outer function has returned

A closure is a nested function that retains access to variables from its enclosing scope, allowing those variables to persist beyond the outer function's lifetime.

What will the following code print? def outer(x): def inner(y): return x + y return inner add5 = outer(5) print(add5(3))

Answer: 8

`outer(5)` returns `inner` with `x` closed over as 5, so calling `add5(3)` computes 5 + 3 = 8.

What is the `nonlocal` keyword used for inside a nested function?

Answer: To modify a variable defined in the nearest enclosing non-global scope

`nonlocal` tells Python that an assignment in the nested function targets the variable in the enclosing scope rather than creating a new local variable.

Which attribute of a function object holds the variables captured by its closure?

Answer: __closure__

`func.__closure__` is a tuple of cell objects, each holding the value of one variable captured from the enclosing scope.

What will this code output? def make_counter(): count = 0 def counter(): nonlocal count count += 1 return count return counter c = make_counter() print(c(), c(), c())

Answer: 1 2 3

Each call to `c()` increments the shared `count` variable via `nonlocal`, producing 1, 2, then 3.

What will the following code print? def outer(): x = 10 def inner(): print(x) x = 20 return inner f = outer() f()

Answer: 20

Closures capture the variable binding (a reference to the cell), not a snapshot of the value at definition time, so `x` is 20 when `inner` runs.

Which of the following is the most common practical use case for closures in Python?

Answer: Factory functions that return specialized functions with pre-configured parameters

Closures are frequently used as factory functions (e.g., `make_adder(n)` returns a function that adds `n`) to produce families of related functions that carry private state.