Timetables for complex schedules in Apache Airflow - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a daily timetable starting at midnight.

Apache Airflow

from airflow.timetables.base import Timetable
class DailyMidnightTimetable(Timetable):
    def infer_manual_data(self, run_after: float):
        return run_after
    def next_dagrun_info(self, last_automated: float | None, now: float) -> float:
        return [1]

Drag options to blanks, or click blank then click option'

Alast_automated + 3600

Bnow + 86400

C(now // 86400 + 1) * 86400

Dnow

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'now + 86400' which schedules at the same time next day, not midnight

Using 'last_automated + 3600' which is hourly from last run

Returning 'now' for immediate execution

The timetable should schedule the next run at midnight the next day (00:00 UTC). Using (now // 86400 + 1) * 86400 calculates the Unix timestamp for the start of the next day using integer division, where 86400 is the number of seconds in a day.

2fill in blank

medium

Complete the code to create a timetable that triggers every Monday at 9 AM.

Apache Airflow

from airflow.timetables.base import Timetable
from datetime import datetime, timedelta
class WeeklyMonday9AMTimetable(Timetable):
    def next_dagrun_info(self, last_automated: float | None, now: float) -> float:
        next_run = datetime.fromtimestamp(now).replace(hour=9, minute=0, second=0, microsecond=0)
        while next_run.weekday() != [1] or next_run.timestamp() <= now:
            next_run += timedelta(days=1)
        return next_run.timestamp()

Drag options to blanks, or click blank then click option'

A0

B4

C6

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1, which is Tuesday, not Monday

Confusing with systems where Sunday is 0

In Python's datetime.weekday() method, Monday is represented by 0, Tuesday by 1, ..., Sunday by 6. The code finds the next Monday at 9 AM after the current time.

3fill in blank

hard

Fix the error in the code to correctly calculate the next run time for a timetable that triggers every hour on the half hour.

Apache Airflow

from airflow.timetables.base import Timetable
from datetime import datetime, timedelta
class HourlyHalfHourTimetable(Timetable):
    def next_dagrun_info(self, last_automated: float | None, now: float) -> float:
        current = datetime.fromtimestamp(now)
        next_run = current.replace(minute=30, second=0, microsecond=0)
        if current.minute >= 30:
            next_run += timedelta(hours=[1])
        return next_run.timestamp()

Drag options to blanks, or click blank then click option'

A0

B1

C30

D60

Attempts:

3 left

💡 Hint

Common Mistakes

Adding 0 hours, leaving next_run in the past

Confusing minutes with hours (30 or 60)

If the current minute is 30 or greater, the half-hour mark today has passed, so advance to the next hour's half-hour by adding 1 hour.

4fill in blank

hard

Fill both blanks to create a timetable that triggers every weekday at 8 AM.

Apache Airflow

from airflow.timetables.base import Timetable
from datetime import datetime, timedelta
class Weekday8AMTimetable(Timetable):
    def next_dagrun_info(self, last_automated: float | None, now: float) -> float:
        next_run = datetime.fromtimestamp(now).replace(hour=[1], minute=0, second=0, microsecond=0)
        while next_run.timestamp() <= now or next_run.weekday() [2] 5:
            next_run += timedelta(days=1)
        return next_run.timestamp()

Drag options to blanks, or click blank then click option'

A8

B<

C>=

D7

Attempts:

3 left

💡 Hint

Common Mistakes

Setting hour to 7 or other value instead of 8

Using '< 5' which skips weekdays (Mon-Fri) instead of weekends

Set the hour to 8 for 8 AM. The loop continues while the time is not in the future or the day is a weekend (weekday() >= 5, where Sat=5, Sun=6), advancing to the next suitable weekday 8 AM.

5fill in blank

hard

Fill all three blanks to create a timetable that triggers on the first day of each month at midnight.

Apache Airflow

from airflow.timetables.base import Timetable
from datetime import datetime, timedelta
class MonthlyFirstDayMidnightTimetable(Timetable):
    def next_dagrun_info(self, last_automated: float | None, now: float) -> float:
        current = datetime.fromtimestamp(now)
        year = current.year
        month = current.month + [1]
        if month > 12:
            month = [2]
            year += 1
        next_run = datetime(year, month, [3], 0, 0, 0)
        return next_run.timestamp()

Drag options to blanks, or click blank then click option'

A1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 for day (invalid date)

Failing to reset month to 1 or increment year on overflow

Adding 0 instead of 1 to month

Add 1 to the current month for the next month. If it exceeds 12, reset month to 1 and increment the year. Use day 1 for the first day of the month, at midnight (hour=0).

Practice

1. What is the main purpose of a timetable in Apache Airflow?

easy

A. To control when workflows (DAGs) are scheduled to run

B. To store data processed by workflows

C. To define the tasks inside a workflow

D. To monitor the status of running tasks

Solution

1. Step 1: Understand Airflow scheduling

   Airflow uses timetables to decide when to start running workflows (DAGs).

2. Step 2: Differentiate timetable from other components

   Timetables do not store data, define tasks, or monitor tasks; they only schedule runs.

3. Final Answer:

   To control when workflows (DAGs) are scheduled to run -> Option A

4. Quick Check:

   Timetable = schedule control [OK]

Hint: Timetables decide when workflows start running [OK]

Common Mistakes:

• Confusing timetable with task definitions
• Thinking timetable stores data
• Mixing timetable with monitoring features

2. Which of the following is the correct way to import the built-in cron timetable in Airflow 2.5+?

easy

A. import airflow.timetables.Cron as CronTimetable

B. import airflow.timetable.cron as CronTimetable

C. from airflow.schedules import CronTimetable

D. from airflow.timetables.cron import CronTimetable

Solution

1. Step 1: Recall Airflow timetable import paths

   Airflow 2.5+ uses airflow.timetables.cron for cron timetable classes.

2. Step 2: Check syntax correctness

   from airflow.timetables.cron import CronTimetable uses correct module and class name with proper Python import syntax.

3. Final Answer:

   from airflow.timetables.cron import CronTimetable -> Option D

4. Quick Check:

   Correct import path = from airflow.timetables.cron import CronTimetable [OK]

Hint: Use airflow.timetables.cron for cron timetable imports [OK]

Common Mistakes:

• Using wrong module name like 'schedules' instead of 'timetables'
• Incorrect capitalization in module or class names
• Wrong import syntax causing errors

3. Given this Airflow timetable code snippet, what schedule does it represent?

from airflow.timetables.cron import CronTimetable
cron = CronTimetable('0 6 * * 1-5')

medium

A. Runs every day at 6:00 AM

B. Runs every hour from 6 AM to 5 PM

C. Runs at 6:00 AM every weekday (Monday to Friday)

D. Runs only on weekends at 6:00 AM

Solution

1. Step 1: Interpret the cron expression '0 6 * * 1-5'

   The fields mean: minute=0, hour=6, day=any, month=any, weekday=1-5 (Monday to Friday).

2. Step 2: Match cron to schedule meaning

   This means the job runs at 6:00 AM on weekdays only.

3. Final Answer:

   Runs at 6:00 AM every weekday (Monday to Friday) -> Option C

4. Quick Check:

   Cron '0 6 * * 1-5' = Weekday 6 AM [OK]

Hint: Cron weekdays 1-5 means Monday to Friday [OK]

Common Mistakes:

• Assuming it runs every day instead of weekdays only
• Confusing hour and minute fields
• Thinking it runs on weekends

4. You wrote this custom timetable code but Airflow raises an error:

class MyTimetable:
    def __init__(self, cron):
        self.cron = cron

my_tt = MyTimetable('0 0 * * *')

What is the likely cause of the error?

medium

A. Not importing CronTimetable from airflow

B. Missing required methods like 'next_dagrun_info' in the timetable class

C. Using a class instead of a function for timetable

D. Incorrect cron string format

Solution

1. Step 1: Understand Airflow timetable requirements

   Custom timetables must implement specific methods like 'next_dagrun_info' to work.

2. Step 2: Check provided class

   The class only stores cron string but lacks required methods, causing Airflow error.

3. Final Answer:

   Missing required methods like 'next_dagrun_info' in the timetable class -> Option B

4. Quick Check:

   Custom timetable needs required methods [OK]

Hint: Custom timetables must implement Airflow's required methods [OK]

Common Mistakes:

• Assuming any class with cron string works as timetable
• Blaming cron string format without checking methods
• Confusing timetable class with task definitions

5. You want to run a DAG every Monday at 8 AM and also on the 1st day of every month at 9 AM. Which Airflow timetable setup correctly combines these schedules?

hard

A. Use a custom timetable that combines two CronTimetable instances for '0 8 * * 1' and '0 9 1 * *', then merges their schedules

B. Create two DAGs, one with '0 8 * * 1' and another with '0 9 1 * *', then combine their runs manually

C. Use a single CronTimetable with expression '0 8 * * 1,0 9 1 * *'

D. Set schedule_interval='@weekly' and add a sensor to trigger on the 1st day of month

Solution

1. Step 1: Understand the scheduling needs

   We need two different schedules: Mondays at 8 AM and 1st day of month at 9 AM.

2. Step 2: Evaluate options for combining schedules

   A single cron expression cannot represent both times simultaneously. Two DAGs is possible but not ideal. A custom timetable combining two CronTimetable instances is the correct approach.

3. Step 3: Why other options fail

   Use a single CronTimetable with expression '0 8 * * 1,0 9 1 * *' is invalid cron syntax. Create two DAGs, one with '0 8 * * 1' and another with '0 9 1 * *', then combine their runs manually is manual and complex. Set schedule_interval='@weekly' and add a sensor to trigger on the 1st day of month uses sensors which is indirect and less clean.

4. Final Answer:

   Use a custom timetable that combines two CronTimetable instances for '0 8 * * 1' and '0 9 1 * *', then merges their schedules -> Option A

5. Quick Check:

   Combine schedules with custom timetable = Use a custom timetable that combines two CronTimetable instances for '0 8 * * 1' and '0 9 1 * *', then merges their schedules [OK]

Hint: Combine multiple cron schedules with a custom timetable class [OK]

Common Mistakes:

• Trying to put two cron expressions in one string
• Creating multiple DAGs instead of one with combined timetable
• Using sensors instead of proper timetable combination