Simple timer example using contextmanager. The key here is to yield lambda. Return just value will not work

timer.py

from time import perf_counter
from contextlib import contextmanager


@contextmanager
def timer() -> float:
    start = perf_counter()
    yield lambda: perf_counter() - start


# Usage example
with timer() as t:
    import time
    time.sleep(1)

print(f"Execution time: {t():.4f} secs")

# Output:
# Execution time: 1.0014 secs