Python: how do I measure how long a piece of code takes?

Question

I want to time a function or a block accurately. `time.time()` differences feel unreliable.

IT-QA Assistant · Accepted Answer

*AI-drafted answer — reviewed for correctness. Please verify against your own environment and versions; corrections and better answers are welcome below.*

Use `time.perf_counter()` — it's a high-resolution monotonic clock, unaffected by system clock changes (unlike `time.time()`):

```python
import time
start = time.perf_counter()
do_work()
print(f"{time.perf_counter() - start:.4f}s")
```

A reusable context manager is cleaner:

```python
from contextlib import contextmanager
@contextmanager
def timer(label):
    t = time.perf_counter()
    yield
    print(f"{label}: {time.perf_counter()-t:.4f}s")

with timer("query"):
    run_query()
```

For micro-benchmarks of small snippets, use `timeit` (it runs many loops and avoids common timing pitfalls): `python -m timeit -s 'setup' 'code'`. To find *where* time goes in a whole program, profile with `python -m cProfile -s cumtime yourscript.py`.

Python: how do I measure how long a piece of code takes?

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