Token counting and cost estimation in Prompt Engineering / GenAI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to count tokens in a text using the tokenizer.

Prompt Engineering / GenAI

tokens = tokenizer.encode(text)
num_tokens = len([1])

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

Atokenizer

Btext

Ctokens

Dencode

Attempts:

3 left

💡 Hint

Common Mistakes

Counting length of the original text string instead of tokens.

The variable tokens holds the list of tokens, so len(tokens) gives the token count.

2fill in blank

medium

Complete the code to calculate the cost given tokens and price per 1000 tokens.

Prompt Engineering / GenAI

cost = (num_tokens / 1000) * [1]

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

Aprice_per_token

Btoken_price

Cnum_tokens

Dprice_per_1000_tokens

Attempts:

3 left

💡 Hint

Common Mistakes

Using price per token instead of price per 1000 tokens.

The cost is calculated by multiplying the number of tokens (in thousands) by the price per 1000 tokens.

3fill in blank

hard

Fix the error in the code to correctly estimate total cost for prompt and completion tokens.

Prompt Engineering / GenAI

total_tokens = prompt_tokens + [1]
cost = (total_tokens / 1000) * price_per_1000_tokens

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

Acompletion_tokens

Bprompt_tokens

Ctoken_count

Dnum_tokens

Attempts:

3 left

💡 Hint

Common Mistakes

Adding prompt tokens twice instead of adding completion tokens.

The total tokens are the sum of prompt tokens and completion tokens, so add completion_tokens.

4fill in blank

hard

Fill both blanks to create a dictionary with token counts and cost per token type.

Prompt Engineering / GenAI

costs = {
    'prompt': prompt_tokens * [1],
    'completion': completion_tokens * [2]
}

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

Aprompt_token_price

Bcompletion_token_price

Cprice_per_token

Dtoken_price

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same price for both token types.

Multiply prompt tokens by their price and completion tokens by their price to get costs per type.

5fill in blank

hard

Fill all three blanks to calculate total cost and print a formatted summary.

Prompt Engineering / GenAI

total_cost = costs['prompt'] + costs[[1]]
summary = f"Prompt tokens cost: ${{costs['prompt']:.4f}}, Completion tokens cost: ${{costs[[2]]:.4f}}, Total cost: $[3]:.4f}}"
print(summary)

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

A'completion'

Ctotal_cost

D'prompt'

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong dictionary keys or variable names in the formatted string.

The total cost adds prompt and completion costs. The summary prints costs for prompt, completion, and total cost.

Practice

1. What is a token in the context of AI language models?

easy

A. A hardware component

B. A small piece of text like a word or part of a word

C. A programming language

D. A type of AI model

Solution

1. Step 1: Understand token meaning

   Tokens are the smallest pieces of text that AI models read, such as words or parts of words.

2. Step 2: Identify correct definition

   Among the options, only A small piece of text like a word or part of a word correctly describes tokens as small text pieces.

3. Final Answer:

   A small piece of text like a word or part of a word -> Option B

4. Quick Check:

   Token = small text piece [OK]

Hint: Tokens are text chunks, not models or hardware [OK]

Common Mistakes:

• Confusing tokens with AI models
• Thinking tokens are programming languages
• Assuming tokens are hardware parts

2. Which of the following Python code snippets correctly counts tokens using a simple split by spaces?

easy

A. tokens = text.split(' ')
count = len(tokens)

B. tokens = text.count(' ')
count = tokens + 1

C. tokens = len(text)
count = tokens

D. tokens = text.split()
count = tokens

Solution

1. Step 1: Understand token counting by splitting

   Splitting text by spaces returns a list of tokens; counting tokens is length of that list.

2. Step 2: Check each option

   tokens = text.split(' ') count = len(tokens) splits by space and counts tokens correctly. tokens = text.count(' ') count = tokens + 1 counts spaces but needs +1 for tokens. tokens = len(text) count = tokens counts characters, not tokens. tokens = text.split() count = tokens assigns list to count, which is incorrect.

3. Final Answer:

   tokens = text.split(' ') count = len(tokens) -> Option A

4. Quick Check:

   Split by space + len() = token count [OK]

Hint: Use split(' ') and len() to count tokens simply [OK]

Common Mistakes:

• Counting characters instead of tokens
• Forgetting to add 1 when counting spaces
• Assigning list directly to count variable

3. Given the text: "Hello world! This is AI." and a token counting method that splits by spaces, what is the token count?

medium

A. 7

B. 6

C. 4

D. 5

Solution

1. Step 1: Split the text by spaces

   Splitting "Hello world! This is AI." by spaces gives: ['Hello', 'world!', 'This', 'is', 'AI.']

2. Step 2: Count the tokens

   There are 5 tokens in the list.

3. Final Answer:

   5 -> Option D

4. Quick Check:

   5 tokens from splitting by space [OK]

Hint: Count words separated by spaces for quick token count [OK]

Common Mistakes:

• Counting punctuation as separate tokens
• Adding extra tokens incorrectly
• Miscounting spaces

4. You wrote this code to count tokens but it gives an error:

text = "AI is fun"
tokens = text.split
count = len(tokens)

What is the error and how to fix it?

medium

A. Missing parentheses in split method call; fix with text.split()

B. len() cannot be used on list; use count() instead

C. text should be a list, not string

D. split method does not exist for strings

Solution

1. Step 1: Identify the error in method call

   text.split is a method reference, not a call. It needs parentheses to execute.

2. Step 2: Fix the code

   Change text.split to text.split() to get the list of tokens, then len() works correctly.

3. Final Answer:

   Missing parentheses in split method call; fix with text.split() -> Option A

4. Quick Check:

   Use split() with parentheses to call method [OK]

Hint: Always add () to call string methods like split() [OK]

Common Mistakes:

• Forgetting parentheses on method calls
• Using len() on method instead of list
• Thinking split is not a string method

5. You want to estimate the cost of an AI request. The model charges $0.0001 per token. If your input has 120 tokens and output is expected to be 80 tokens, what is the total estimated cost?

hard

A. $0.012

B. $0.01

C. $0.02

D. $0.008

Solution

1. Step 1: Calculate total tokens used

   Total tokens = input tokens + output tokens = 120 + 80 = 200 tokens.

2. Step 2: Multiply total tokens by cost per token

   Cost = 200 tokens * $0.0001 = $0.02.

3. Step 3: Check options carefully

   $0.02 shows $0.02, but $0.012 shows $0.012 which is incorrect. Recalculate carefully: 200 * 0.0001 = 0.02, so $0.02 is correct.

4. Final Answer:

   $0.02 -> Option C

5. Quick Check:

   200 tokens * $0.0001 = $0.02 [OK]

Hint: Add input and output tokens, multiply by cost per token [OK]

Common Mistakes:

• Multiplying only input tokens by cost
• Multiplying only output tokens by cost
• Misreading decimal places in cost