Late-Binding in Closures: A Common Trap

Lambdas defined inside loops often capture the loop variable by reference. We walk through the trace and show a safe pattern to capture the current value.

funcs = [lambda: i for i in range(3)]
print([f() for f in funcs])  # prints [2,2,2]

Why it prints [2,2,2]

The lambda captures the name `i`, not its value at definition time. When the lambdas run, `i` has the final loop value (2), so each lambda returns 2.

Fix: capture by default parameter

funcs = [lambda i=i: i for i in range(3)]
print([f() for f in funcs])  # prints [0,1,2]