Easy Leasy

Easy Leasy is a Python library for defining time-based rules and manipulating time sets.

The idea is to express easily things like "open from 9am to 5pm from Monday to Friday" as a single expression, and then use it both to know if a given time is in the time set, and to compute the next time change.

Usage

You can use the parse_easy_leasy function to parse an expression into a BaseTimeSet object, which will allow you query that time set.

from easy_leasy import parse_easy_leasy
from datetime import datetime
from zoneinfo import ZoneInfo

p = parse_easy_leasy(
    """
    from context import has_pr

    let work_hour be when 9:30~13:30 | 14:30~18:30
    let work_day be when mon | tue | wed | thu | fri
    let business_hour be when work_hour & work_day

    let xmas be when 25 & dec
    let ny be when 1 & jan
    let work be when 1 & may
    let holiday be when xmas | ny | work

    return business_hour - holiday
    """,
    dict(has_pr=True),
)

now = datetime.now(tz=ZoneInfo("Europe/Paris"))
print(p.value_at(now))
print(p.next_change(now))

The parse_easy_leasy function takes two arguments: the expression to parse, and a dictionary of context variables which can either be a boolean or a BaseTimeSet object.

Language reference

The language is simple and has 3 different statements:

• from <namespace> import <name>: import a variable from the context.
• let <name> be when <expression>: declare a new variable <name> with the value of <expression>.
• return <expression>: return the value of <expression>.

The only statement that is mandatory is return, which is the expression that will be evaluated to determine the value of the time set.

Expressions are composed of the different types:

• Hour ranges: hour:minute~hour:minute
• Days of the week: mon | tue | wed | thu | fri | sat | sun
• Days of the month: 1 | 2 | ... | 31
• Months: jan | feb | ... | dec
• Absolutes: always | never

These expressions can be combined using the same operators as the Python sets:

• |: union
• &: intersection
• -: difference
• ~: complement

API reference

Everything is based on the BaseTimeSet class, which can also be used directly from Python.

It has different implementations, which are:

• Always: always true
• Never: always false
• HourRange: a range of hours
• Day: a single day of the week
• WeekDay: a single day of the month
• Month: a single month
• Constant: a constant value

As they are subclasses of BaseTimeSet, they can be used with the standard Python set operators, for example:

from easy_leasy import Always, Month

p = Always() & Month('jan')

Once you have a BaseTimeSet object, you can use the value_at and next_change methods to query the time set.

from easy_leasy import Always
from datetime import datetime
from zoneinfo import ZoneInfo

p = Always()

# Check if the time set is true at a given instant
p.value_at(datetime.now(tz=ZoneInfo("Europe/Paris")))

# Get the next time change
p.next_change(datetime.now(tz=ZoneInfo("Europe/Paris")))