Get recurring event instances

[dmitrysync]

Hi.
Please suggest how to quickly get all instances of a recurring event.

My versions are slow.

Version 01:

from datetime import datetime, timezone as timezones

from exchangelib import (
    Account as ExchangeAccount,
    Configuration,
    Credentials,
    DELEGATE,
    FolderCollection,
    NTLM,
)

from exchangelib.errors import (
    ErrorCalendarOccurrenceIndexIsOutOfRecurrenceRange,
    ErrorCalendarOccurrenceIsDeletedFromRecurrence,
)

def get_recurring_event_instances(server, email, password, calendar_id, event_id, start_ts, end_ts):
    auth_type = NTLM
    if not server:
        autodiscover = True
        auth_type = None

    credentials = Credentials(username=email, password=password)
    config = Configuration(server=server, credentials=credentials, auth_type=auth_type)

    account = ExchangeAccount(
        primary_smtp_address=email,
        config=config,
        autodiscover=autodiscover,
        access_type=DELEGATE,
    )

    fc = FolderCollection(account=account, folders=[account.calendar])

    calendar = None
    if fc:
        for folder in fc:
            if folder.id == calendar_id:
                calendar = folder

            for child in folder.children:
                if child.id == calendar_id:
                    calendar = child

    start = datetime.fromtimestamp(start_ts, tz=timezones.utc)
    end = datetime.fromtimestamp(end_ts, tz=timezones.utc)

    master_recurrence = calendar.get(id=event_id)
    index = 1
    instances = []
    while True:
        occurrence = master_recurrence.occurrence(index)
        try:
            occurrence.refresh()
        except ErrorCalendarOccurrenceIndexIsOutOfRecurrenceRange:
            break
        except ErrorCalendarOccurrenceIsDeletedFromRecurrence:
            index += 1
            continue

        if occurrence.start < start:
            index += 1
            continue

        if occurrence.start > end:
            break

        instances.append(occurrence)
        index += 1

    return instances

Version 02:

from exchangelib import (
    Account as ExchangeAccount,
    Configuration,
    Credentials,
    DELEGATE,
    FolderCollection,
    NTLM,
)

def get_recurring_event_instances(server, email, password, calendar_id, event_id, start_ts, end_ts):
    auth_type = NTLM
    if not server:
        autodiscover = True
        auth_type = None

    credentials = Credentials(username=email, password=password)
    config = Configuration(server=server, credentials=credentials, auth_type=auth_type)

    account = ExchangeAccount(
        primary_smtp_address=email,
        config=config,
        autodiscover=autodiscover,
        access_type=DELEGATE,
    )

    fc = FolderCollection(account=account, folders=[account.calendar])

    calendar = None
    if fc:
        for folder in fc:
            if folder.id == calendar_id:
                calendar = folder

            for child in folder.children:
                if child.id == calendar_id:
                    calendar = child

    master_recurrence = calendar.get(id=event_id)
    instances = []
    if calendar:
        events = list(
            calendar.view(
                start=datetime.fromtimestamp(start_ts, tz=account.default_timezone),
                end=datetime.fromtimestamp(end_ts, tz=account.default_timezone),
            ),
        )

        for event in events:
            if event.type == 'Occurrence' or event.type == 'Exception':
                recurring_master = event.recurring_master()

                if recurring_master._id.changekey == master_recurrence._id.changekey:
                    instances.append(event)

    return instances

[ecederstrand]

If you have a single master occurrence, then master_recurrence.occurrence(index) is the easiest way to get to each occurrence. If you need to optimize that, then you'll need to go a bit more low-level so you wan bulk fetch the occurrences, limit the fields to fetch, etc.

If you just want to access occurrences in the calendar instead of recurring items, then use the account.calendar.view() method.

[dmitrysync]

Can you suggest how to make a bulk fetching of the occurrences?

[ecederstrand]

.occurrence() doesn't actually fetch the item from the server, it just creates an object prepared for that. So use this method to create the objects you want to fetch in bulk, and then use account.fetch() to fetch the created items in bulk, optionally restricting the fields to fetch.

[dmitrysync]

How to find out the number of occurrences?

[ecederstrand]

There's probably more than one way to do it, but you could calculate the number from the recurrence specification in CalendarItem.recurrence, and subtract the occurrences mentioned in CalendarItem.deleted_occurrences.

[dmitrysync]

Thanks!