# Quickstart: Python

URL: https://workclock.karthik.nz/docs/quickstart/python.md

By the end of this page you will have a Python program that works out when a support ticket is due, counting only working hours, and how much of its SLA has been used.

## Install

workclock needs CPython 3.9 or later. Install it with pip, or add it to a uv project:

**pip**

```sh
pip install workclock
```

**uv**

```sh
uv add workclock
```

On Windows, also install the `tzdata` package: the program builds its datetimes with the standard library's `zoneinfo.ZoneInfo`, which needs it there ([Install: Time zone data](https://workclock.karthik.nz/docs/install.md#time-zone-data)).

## Write the program

A support desk in London works 09:00–17:00 on weekdays with a lunch hour, and is closed on 25 and 28 December 2026. A ticket opened at 16:30 on Christmas Eve with an 8-hour SLA is due at 09:30 on 30 December. At 11:00 on 29 December, 2 hours 30 minutes of the SLA have been used.

In Python, save this as `sla.py`:

```python title="sla.py"
from datetime import date, datetime, time
from zoneinfo import ZoneInfo

from workclock import Break, Holidays, Schedule, WorkDay

london = ZoneInfo("Europe/London")
support = Schedule(
    [
        WorkDay(time(9), time(17)),  # Monday to Friday by default
        Break(time(12), time(13)),
        Holidays([date(2026, 12, 25), date(2026, 12, 28)]),
    ],
    time_zone=london,
)

opened = datetime(2026, 12, 24, 16, 30, tzinfo=london)
due = support.add(opened, hours=8)  # 2026-12-30 09:30, London time
now = datetime(2026, 12, 29, 11, tzinfo=london)
used = support.between(opened, now)  # 2:30:00

print(f"due {due}, used {used}")
```

## Run it

**pip**

```sh
python sla.py
```

**uv**

```sh
uv run sla.py
```

It prints:

```text
due 2026-12-30 09:30:00+00:00, used 2:30:00
```

London time is UTC+00:00 in December, so the due time is 09:30 London time:



## What just happened

`workclock.Schedule` combined three rules, read in the `Europe/London` time zone: a `WorkDay` rule for 09:00–17:00 on Monday to Friday, a `Break` rule for 12:00–13:00, and a `Holidays` rule for 25 and 28 December. `support.add` counted 8 hours of working time from the moment the ticket was opened, skipping the evening, the weekend, the holidays and the lunch hour, and returned an aware `datetime` with the same `tzinfo` as `opened`. `support.between` returned the working time between two datetimes as a `timedelta`. [`examples/python/sla.py`](https://github.com/Karthik-beta/workclock/blob/main/examples/python/sla.py) extends this program with `next_period`, which finds when the current stretch of working time ends, and `add_many`, which computes many due times in one call.

## Next steps

- [Schedules](https://workclock.karthik.nz/docs/concepts/schedules.md): how rules combine into working time.
- [Migrating from businesstimedelta](https://workclock.karthik.nz/docs/guides/migrating-from-businesstimedelta.md): run existing businesstimedelta code on `workclock.compat`, and where it differs.