Sharing data between tasks effectively in Apache Airflow - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push data from one task to XCom in Airflow.

Apache Airflow

def push_function(ti):
    ti.[1](key='sample_key', value='Hello from task')

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

Apush_xcom

Bxcom_push

Cxcom_pull

Dsend_xcom

Attempts:

3 left

💡 Hint

Common Mistakes

Using xcom_pull instead of xcom_push to send data.

Using incorrect method names like push_xcom or send_xcom.

The xcom_push method is used to send data from a task to XCom in Airflow.

2fill in blank

medium

Complete the code to pull data from XCom in Airflow.

Apache Airflow

def pull_function(ti):
    value = ti.[1](key='sample_key', task_ids='push_task')
    print(value)

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

Axcom_push

Bget_xcom

Cpull_xcom

Dxcom_pull

Attempts:

3 left

💡 Hint

Common Mistakes

Using xcom_push instead of xcom_pull to get data.

Using incorrect method names like pull_xcom or get_xcom.

The xcom_pull method is used to retrieve data from XCom in Airflow.

3fill in blank

medium

Complete the code to push data to XCom in Airflow.

Apache Airflow

def push_function(ti):
    ti.[1]('sample_key', 'Data to share')

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

Axcom_push

Bxcom_pull

Cpush_xcom

Dsend_xcom

Attempts:

3 left

💡 Hint

Common Mistakes

Using xcom_pull instead of xcom_push to send data.

Using incorrect method names like push_xcom or send_xcom.

The xcom_push method is used to send data from a task to XCom in Airflow.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that shares only even numbers via XCom.

Apache Airflow

result = {num: num[1]2 for num in range(1, 6) if num [2] 2 == 0}

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

A**

B%

C//

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect operators like + or // in the comprehension.

Using wrong condition to filter even numbers.

The expression num**2 squares the number, and num % 2 == 0 filters even numbers.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that shares uppercase keys with values greater than zero via XCom.

Apache Airflow

result = { [1]: [2] for [3], v in data.items() if v > 0}

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

Ak.upper()

Bv

Ck

Dv.upper()

Attempts:

3 left

💡 Hint

Common Mistakes

Using v.upper() which is invalid if values are not strings.

Mixing up keys and values in the comprehension.

The key is converted to uppercase with k.upper(), the value is v, and the loop variable is k.

Practice

1. What is the primary purpose of using Airflow Variables when sharing data between tasks?

easy

A. To execute tasks in parallel

B. To monitor task execution logs

C. To schedule DAG runs automatically

D. To store small pieces of data accessible across different tasks

Solution

1. Step 1: Understand Airflow Variables role

   Airflow Variables are designed to hold small data values that can be shared between tasks.

2. Step 2: Identify the correct use case

   Sharing data between tasks requires a storage mechanism accessible by all tasks, which Airflow Variables provide.

3. Final Answer:

   To store small pieces of data accessible across different tasks -> Option D

4. Quick Check:

   Airflow Variables = data sharing [OK]

Hint: Variables store shared data between tasks easily [OK]

Common Mistakes:

• Confusing Variables with task scheduling
• Thinking Variables execute tasks
• Using Variables for logging

2. Which of the following is the correct way to set an Airflow Variable named my_var with value 123 inside a PythonOperator task?

easy

A. Variable.set('my_var', 123)

B. Variable.set(my_var, '123')

C. Variable.get('my_var', 123)

D. Variable.create('my_var', 123)

Solution

1. Step 1: Recall Variable.set syntax

   The correct method to set a variable is Variable.set(key, value) where key is a string and value is the data.

2. Step 2: Check option correctness

   Variable.set('my_var', 123) uses Variable.set with key 'my_var' and value 123 correctly as a string key and integer value.

3. Final Answer:

   Variable.set('my_var', 123) -> Option A

4. Quick Check:

   Set variable = Variable.set(key, value) [OK]

Hint: Use Variable.set('key', value) to store data [OK]

Common Mistakes:

• Using Variable.get instead of set to store data
• Not quoting the variable name key
• Using a non-existent method like Variable.create

3. Given the following code snippet in two tasks, what will be printed by task_b?

from airflow.models import Variable

def task_a():
    Variable.set('shared_key', 'hello')

def task_b():
    value = Variable.get('shared_key')
    print(value)

medium

A. None

B. hello

C. shared_key

D. Error: Variable not found

Solution

1. Step 1: Analyze task_a behavior

   task_a sets the Variable 'shared_key' with value 'hello'.

2. Step 2: Analyze task_b behavior

   task_b retrieves the Variable 'shared_key' and prints its value, which is 'hello'.

3. Final Answer:

   hello -> Option B

4. Quick Check:

   Set then get Variable = 'hello' [OK]

Hint: Get returns the stored value by key [OK]

Common Mistakes:

• Expecting the key name instead of value
• Assuming Variable.get returns None if set
• Forgetting to set the Variable before getting

4. You wrote this code in task_b to get a Variable set by task_a:

value = Variable.get('my_var')

But you get an error: KeyError: 'Variable my_var does not exist'. What is the best fix?

medium

A. Set a default value in Variable.get like Variable.get('my_var', default_var='default')

B. Change Variable.get to Variable.set

C. Remove the Variable.get call

D. Restart Airflow scheduler

Solution

1. Step 1: Understand the error cause

   The error means 'my_var' was not set before getting it, so Variable.get fails.

2. Step 2: Use default value to avoid error

   Variable.get supports a default_var parameter to return if key missing, preventing KeyError.

3. Final Answer:

   Set a default value in Variable.get like Variable.get('my_var', default_var='default') -> Option A

4. Quick Check:

   Use default_var to avoid missing key error [OK]

Hint: Add default_var to Variable.get to prevent errors [OK]

Common Mistakes:

• Using Variable.set instead of get to read data
• Ignoring missing Variable errors
• Restarting scheduler without fixing code

5. You want to share a list of user IDs between two tasks in Airflow. Which approach is best to share this data effectively?

hard

A. Write the list to a local file and read it in the next task

B. Pass the list directly as a Python variable between tasks

C. Use XComs to push and pull the list between tasks

D. Serialize the list as JSON string and store it in an Airflow Variable

Solution

1. Step 1: Understand data sharing options

   Airflow Variables are for small strings; passing Python variables directly is not possible between tasks.

2. Step 2: Identify best practice for complex data

   XComs are designed to share data like lists between tasks efficiently and safely.

3. Final Answer:

   Use XComs to push and pull the list between tasks -> Option C

4. Quick Check:

   XComs = best for task-to-task data sharing [OK]

Hint: Use XComs for complex data sharing between tasks [OK]

Common Mistakes:

• Trying to pass Python variables directly
• Using Variables for large or complex data
• Using local files which break portability