LangChain Expression Language (LCEL) basics - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this LCEL expression?

Given the LCEL expression "Hello, {user.name}! Today is {date.today()}", what will be the output if user.name is "Alice" and today's date is 2024-06-15?

A "Hello, {user.name}! Today is {date.today()}"

B "Hello, Alice! Today is 2024-06-15"

C "Hello, Alice! Today is {date.today()}"

D "Hello, user.name! Today is 2024-06-15"

💡 Hint

LCEL replaces expressions inside curly braces with their evaluated values.

LCEL evaluates expressions inside curly braces. Here, {user.name} becomes 'Alice' and {date.today()} returns the current date '2024-06-15'.

📝 Syntax

intermediate

Which LCEL expression is syntactically correct?

Choose the LCEL expression that is valid and will not cause a syntax error.

A "Sum is {a + b}"

B "Sum is a + b}"

C "Sum is {a + b"

D "Sum is {a + }"

💡 Hint

Check for balanced braces and complete expressions inside curly braces.

Option A has a complete expression inside balanced braces. Options A, B, and C have syntax errors due to incomplete or unbalanced braces.

❓ state_output

advanced

What is the value of variable result after evaluating this LCEL expression?

Given variables a = 5 and b = 3, what is the value of result after evaluating "{a > b ? 'a is greater' : 'b is greater or equal'}"?

A "a is greater"

B "b is greater or equal"

C true

D false

💡 Hint

LCEL supports ternary expressions inside curly braces.

Since a (5) is greater than b (3), the condition is true, so the expression returns 'a is greater'.

🔧 Debug

advanced

Which option causes a runtime error when evaluating this LCEL expression?

Consider the LCEL expression "User age: {user.age}". Which option will cause a runtime error if user does not have an age property?

A "User age: {user.age ?? 'unknown'}"

B "User age: {user?.age}"

C "User age: {user.age}"

D "User age: {user.get('age', 'unknown')}"

💡 Hint

Check how missing properties are accessed safely in LCEL.

Option C tries to access a missing property directly, causing a runtime error. Options B, C, and D use safe access or default values to avoid errors.

🧠 Conceptual

expert

How many items are in the resulting list after evaluating this LCEL expression?

Given numbers = [1, 2, 3, 4], what is the length of the list produced by [n * 2 for n in numbers if n % 2 == 0] in LCEL?

A 1

B 4

C 3

D 2

💡 Hint

Filter numbers that are even, then multiply by 2.

Only 2 and 4 are even in the list, so the resulting list has 2 items: [4, 8].