Basic usage
Input
f = limit_calls(2)(lambda x: x + 1); f(3)
Output
4
f is allowed 2 calls. The first call returns 3 + 1 = 4.
Full lesson preview
Create a Decorator That Limits the Number of Calls
Implement a decorator factory that limits how many times a function can be called and returns a default value thereafter.
Python practice25 minDecorators FundamentalsAdvancedLast updated April 15, 2026
Problem statement
Write a decorator factory limit_calls(max_calls, *, default=None) which returns a decorator. When applied to a function, the resulting wrapped function should only allow up to max_calls successful calls. After the limit is reached, further calls should return the provided default value. The wrapper must expose a .remaining attribute showing how many calls remain, and a .reset() method to restore the remaining count back to max_calls.
Requirements:
- The decorator factory accepts a non-negative integer max_calls and an optional keyword-only default value (default=None).
- Each decorated function maintains its own independent counter.
- Use functools.wraps (or equivalent) so wrapped function preserves name and docstring.
- The wrapper must provide wrapper.remaining (an integer) and wrapper.reset() to reset the counter.
- If max_calls == 0, the wrapped function should return the default on every call until reset is used.
Task
Build a reusable decorator limit_calls(max_calls, *, default=None) that: enforces a call limit, exposes remaining calls, and supports resetting the counter.
Examples
Exceeding the limit returns default
Input
(g := limit_calls(1, default='X')(lambda: 'ok'), g(), g())[2]
Output
X
g is allowed 1 successful call (returns 'ok'); the second call returns the default 'X'.
Input format
You will implement the function limit_calls(max_calls, *, default=None). Test inputs create and call decorated functions; each test is a single expression evaluated after your code.
Output format
Each test expression should evaluate to a value (or None). The harness compares str(value) to the expected string.
Constraints
max_calls is a non-negative integer. Do not use external libraries. Use functools.wraps to preserve metadata. The wrapper must expose .remaining (int) and .reset() (callable).
Samples
Sample 1
Input
f = limit_calls(2)(lambda x: x*2); f(5)
Output
10
Two calls allowed; first call returns 5*2 = 10.