SCAN for safe key iteration in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start scanning keys from the beginning.

Redis

cursor = [1]

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

ANone

B0

C-1

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting cursor at 1 instead of 0.

Using None or negative numbers as cursor.

The SCAN command starts with cursor 0 to begin iteration over keys.

2fill in blank

medium

Complete the code to scan keys matching the pattern 'user:*'.

Redis

cursor, keys = redis.scan(cursor, match=[1])

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

A'user*'

B'user#*'

C'user:*'

D'user?*'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'user*' which matches keys starting with 'user' but no colon.

Using incorrect wildcard characters like '?' or '#'.

The pattern 'user:*' matches keys starting with 'user:' followed by anything.

3fill in blank

hard

Fix the error in the loop condition to continue scanning until cursor is zero.

Redis

while cursor != [1]:
    cursor, keys = redis.scan(cursor)

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

A0

B-1

CNone

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for cursor != None or -1 which are invalid.

Using cursor != 1 which causes infinite loop.

The SCAN command returns cursor 0 when the iteration is complete.

4fill in blank

hard

Fill both blanks to scan keys with count 100 and match pattern 'session:*'.

Redis

cursor, keys = redis.scan(cursor, match=[1], count=[2])

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

A'session:*'

B50

C100

D'user:*'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong match pattern like 'user:*'.

Setting count to 50 instead of 100.

Use match='session:*' to filter keys and count=100 to limit keys per scan.

5fill in blank

hard

Fill all three blanks to safely iterate all keys and collect them in a list.

Redis

all_keys = []
cursor = [1]
while cursor != [2]:
    cursor, keys = redis.scan(cursor, match=[3])
    all_keys.extend(keys)

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

A0

BNone

C'*'

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using None or 1 as cursor start or end condition.

Using a match pattern other than '*'.

Start cursor at 0, loop until cursor is 0, and match '*' to get all keys.