Why XCom enables task communication in Apache Airflow - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push a value to XCom in an Airflow task.

Apache Airflow

ti.[1](key='sample_key', value='hello')

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

Axcom_push

Bpush_xcom

Csend

Dpull

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pull' instead of 'xcom_push' to send data.

Using incorrect method names like 'push_xcom'.

The method xcom_push is used to send data from one task to another in Airflow.

2fill in blank

medium

Complete the code to pull a value from XCom in an Airflow task.

Apache Airflow

value = ti.[1](key='sample_key', task_ids='task_a')

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

Axcom_push

Bpull_xcom

Cxcom_pull

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'xcom_push' instead of 'xcom_pull' to get data.

Using incorrect method names like 'pull_xcom'.

The method xcom_pull retrieves data sent by another task via XCom.

3fill in blank

hard

Fix the error in the code to correctly pull XCom data from a specific task.

Apache Airflow

result = ti.xcom_pull(key=[1], task_ids='task_b')

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

A'result_key'

Bresult_key

C['result_key']

D"result_key"

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the key without quotes causing a NameError.

Passing the key as a list instead of a string.

The key parameter must be a string, so it needs quotes. Double quotes or single quotes both work.

4fill in blank

hard

Fill both blanks to push and then pull a value using XCom in Airflow.

Apache Airflow

ti.[1](key='data', value=42)
retrieved = ti.[2](key='data', task_ids='task_c')

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

Axcom_push

Bxcom_pull

Cpush

Dpull

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up push and pull methods.

Using non-existent methods like 'push' or 'pull' alone.

Use xcom_push to send data and xcom_pull to receive it.

5fill in blank

hard

Fill all three blanks to create a dictionary comprehension that pulls XCom values greater than 10.

Apache Airflow

results = {task_id: ti.[1](key='value', task_ids=task_id) for task_id in tasks if ti.[2](key='value', task_ids=task_id) [3] 10}

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

Axcom_pull

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using different methods for pulling data in the comprehension.

Using '<' instead of '>' for filtering.

Use xcom_pull to get values and filter those greater than 10 with >.

Practice

1. What is the main purpose of XCom in Airflow?

easy

A. To store large files generated by tasks

B. To schedule tasks at specific times

C. To monitor the health of Airflow workers

D. To enable tasks to share small pieces of data between each other

Solution

1. Step 1: Understand XCom's role in Airflow

   XCom is designed to let tasks exchange small data easily during a workflow.

2. Step 2: Compare options with XCom's purpose

   Scheduling tasks, monitoring workers, or storing large files are not XCom's functions.

3. Final Answer:

   To enable tasks to share small pieces of data between each other -> Option D

4. Quick Check:

   XCom = task data sharing [OK]

Hint: XCom is for small data sharing between tasks [OK]

Common Mistakes:

• Confusing XCom with scheduling features
• Thinking XCom stores large files
• Mixing XCom with monitoring tools

2. Which Airflow method is used to send data from one task to another using XCom?

easy

A. xcom_pull()

B. xcom_push()

C. send_data()

D. push_xcom()

Solution

1. Step 1: Identify the method to send data in XCom

   The method to send data is called xcom_push().

2. Step 2: Verify other options

   xcom_pull() is for receiving data, and the others are not valid Airflow methods.

3. Final Answer:

   xcom_push() -> Option B

4. Quick Check:

   Send data = xcom_push() [OK]

Hint: Push data with xcom_push(), pull with xcom_pull() [OK]

Common Mistakes:

• Confusing xcom_push() with xcom_pull()
• Using non-existent methods like send_data()
• Mixing method names

3. Given the following code snippet in Airflow tasks:

def task_a(ti):
    ti.xcom_push(key='result', value=42)

def task_b(ti):
    value = ti.xcom_pull(key='result', task_ids='task_a')
    print(value)

What will task_b print when executed?

medium

A. 42

B. None

C. task_a

D. Error

Solution

1. Step 1: Understand xcom_push and xcom_pull usage

   task_a pushes the value 42 with key 'result'. task_b pulls this value using the same key and task_id.

2. Step 2: Determine the printed output

   Since task_b pulls the value 42 correctly, it will print 42.

3. Final Answer:

   42 -> Option A

4. Quick Check:

   Push 42, pull 42 = print 42 [OK]

Hint: Pull what was pushed with matching key and task_id [OK]

Common Mistakes:

• Expecting None if keys don't match
• Confusing task_ids parameter
• Assuming print outputs task name

4. In the code below, why does task_b print None instead of the expected value?

def task_a(ti):
    ti.xcom_push(key='data', value='hello')

def task_b(ti):
    value = ti.xcom_pull(key='result', task_ids='task_a')
    print(value)

medium

A. xcom_pull requires a different method signature

B. The task_ids parameter is incorrect

C. The key used in xcom_pull does not match the key used in xcom_push

D. xcom_push cannot send strings

Solution

1. Step 1: Compare keys used in push and pull

   task_a pushes with key 'data', but task_b pulls with key 'result'. This mismatch causes None to be returned.

2. Step 2: Verify other parameters

   task_ids is correct, xcom_push supports strings, and method signature is valid.

3. Final Answer:

   The key used in xcom_pull does not match the key used in xcom_push -> Option C

4. Quick Check:

   Matching keys needed for XCom data [OK]

Hint: Keys must match exactly in push and pull [OK]

Common Mistakes:

• Ignoring key name mismatch
• Assuming xcom_push can't send strings
• Changing task_ids unnecessarily

5. You want to pass a list of numbers from task_a to task_b using XCom. Which approach correctly enables this communication?

hard

A. In task_a: ti.xcom_push(key='numbers', value=[1, 2, 3])In task_b: nums = ti.xcom_pull(key='numbers', task_ids='task_a')

B. In task_a: ti.xcom_push(key='numbers', value='1,2,3')In task_b: nums = ti.xcom_pull(key='numbers', task_ids='task_b')

C. In task_a: ti.xcom_push(key='data', value=[1, 2, 3])In task_b: nums = ti.xcom_pull(key='numbers', task_ids='task_a')

D. In task_a: ti.xcom_push(value=[1, 2, 3])In task_b: nums = ti.xcom_pull(key='numbers', task_ids='task_a')

Solution

1. Step 1: Check key and value consistency

   In task_a: ti.xcom_push(key='numbers', value=[1, 2, 3])
   In task_b: nums = ti.xcom_pull(key='numbers', task_ids='task_a') uses the same key 'numbers' in push and pull, and passes a list correctly.

2. Step 2: Verify task_ids and value types

   Other options fail: one pushes a string '1,2,3' instead of list and pulls from wrong task_id 'task_b'; another mismatches keys 'data' vs 'numbers'; another omits key in push (defaults to 'return_value') but uses key='numbers' in pull.

3. Final Answer:

   In task_a: ti.xcom_push(key='numbers', value=[1, 2, 3])
   In task_b: nums = ti.xcom_pull(key='numbers', task_ids='task_a') -> Option A

4. Quick Check:

   Matching keys and task_ids with correct value type [OK]

Hint: Use same key and task_id, push list directly [OK]

Common Mistakes:

• Mismatching keys between push and pull
• Pulling from wrong task_id
• Omitting key parameter in push or pull