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Rest APIprogramming~5 mins

Human-readable error messages in Rest API - Time & Space Complexity

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Time Complexity: Human-readable error messages
O(n)
Understanding Time Complexity

When creating human-readable error messages in a REST API, it's important to know how the time to generate these messages changes as the number of errors grows.

We want to understand how the work needed to prepare error messages increases with more errors.

Scenario Under Consideration

Analyze the time complexity of the following code snippet.

def format_errors(errors):
    messages = []
    for error in errors:
        message = f"Error {error['code']}: {error['message']}"
        messages.append(message)
    return messages

This code takes a list of error objects and creates a list of readable error messages.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

  • Primary operation: Looping through each error in the list.
  • How many times: Once for each error in the input list.
How Execution Grows With Input

As the number of errors increases, the time to create messages grows in a straight line.

Input Size (n)Approx. Operations
1010 message creations
100100 message creations
10001000 message creations

Pattern observation: Doubling the number of errors doubles the work needed to create messages.

Final Time Complexity

Time Complexity: O(n)

This means the time to create error messages grows directly with the number of errors.

Common Mistake

[X] Wrong: "Creating error messages takes the same time no matter how many errors there are."

[OK] Correct: Each error needs its own message, so more errors mean more work and more time.

Interview Connect

Understanding how error message creation scales helps you write APIs that stay responsive even when many errors occur. This skill shows you can think about performance in real situations.

Self-Check

"What if we combined all error messages into one string instead of a list? How would the time complexity change?"

Practice

(1/5)
1.

What is the main purpose of human-readable error messages in a REST API?

easy
A. To confuse users with complex codes
B. To hide all error details from users
C. To make error messages as technical as possible
D. To explain problems in simple words for users

Solution

  1. Step 1: Understand the role of error messages

    Error messages should help users understand what went wrong.

  2. Step 2: Identify the best description

    Human-readable means simple and clear, not technical or confusing.

  3. Final Answer:

    To explain problems in simple words for users -> Option D

  4. Quick Check:

    Human-readable = simple explanation [OK]
Hint: Think: error messages should help, not confuse [OK]
Common Mistakes:
  • Choosing technical jargon instead of simple words
  • Assuming error messages should hide details
  • Confusing human-readable with code-only messages
2.

Which of the following is the correct JSON format for a human-readable error message in a REST API response?

{
  "error": {
    "code": 404,
    "message": "Resource not found"
  }
}
easy
A. { error: 404, message: 'Not found' }
B. { "error": { "code": 404, "message": "Resource not found" } }
C. { "code": 404, "msg": "Not found" }
D. { error_code: 404, error_message: 'Resource missing' }

Solution

  1. Step 1: Check JSON syntax correctness

    Valid JSON requires double quotes around keys and string values.

  2. Step 2: Match the expected structure

    The error object should contain code and message keys with clear names.

  3. Final Answer:

    { "error": { "code": 404, "message": "Resource not found" } } -> Option B

  4. Quick Check:

    Valid JSON with clear keys = { "error": { "code": 404, "message": "Resource not found" } } [OK]
Hint: Look for double quotes and clear key names in JSON [OK]
Common Mistakes:
  • Using single quotes instead of double quotes in JSON
  • Missing nested error object structure
  • Using incorrect key names like 'msg' or 'error_code'
3.

Given this API response code snippet, what will be the output message?

response = {
  "status": 400,
  "error": {
    "code": "INVALID_INPUT",
    "message": "Input value is not valid"
  }
}
print(response["error"]["message"])
medium
A. Input value is not valid
B. 400
C. INVALID_INPUT
D. KeyError

Solution

  1. Step 1: Access nested dictionary keys

    response["error"] gives the nested dictionary, then ["message"] accesses the message string.

  2. Step 2: Print the message value

    The value of response["error"]["message"] is "Input value is not valid".

  3. Final Answer:

    Input value is not valid -> Option A

  4. Quick Check:

    Nested key access = message string [OK]
Hint: Follow dictionary keys step-by-step to find the message [OK]
Common Mistakes:
  • Printing the error code instead of message
  • Confusing status code with error message
  • Trying to access keys incorrectly causing KeyError
4.

Identify the error in this REST API error response JSON and fix it for proper human-readable message format:

{
  error: {
    code: 401,
    message: 'Unauthorized access'
  }
}
medium
A. Remove the error object and keep only code and message
B. Change code 401 to string '401'
C. Replace single quotes with double quotes and add quotes around keys
D. Add a status key with value 'error'

Solution

  1. Step 1: Check JSON syntax rules

    JSON keys and string values must be in double quotes, not single quotes or unquoted.

  2. Step 2: Fix the JSON format

    Add double quotes around keys (error, code, message) and change single quotes to double quotes.

  3. Final Answer:

    Replace single quotes with double quotes and add quotes around keys -> Option C

  4. Quick Check:

    Valid JSON needs double quotes on keys and strings [OK]
Hint: JSON keys and strings always need double quotes [OK]
Common Mistakes:
  • Using single quotes for strings in JSON
  • Leaving keys unquoted causing syntax errors
  • Changing numeric codes to strings unnecessarily
5.

You want to design a REST API error response that helps users fix input errors quickly. Which approach is best?

{
  "error": {
    "code": "INVALID_EMAIL",
    "message": "Email format is incorrect",
    "field": "email",
    "suggestion": "Use a valid email like user@example.com"
  }
}
hard
A. Include error code, message, field name, and suggestion for fix
B. Only include a generic error message without details
C. Return HTTP 200 status with error details inside
D. Send error details only in server logs, not in response

Solution

  1. Step 1: Identify helpful error response elements

    Clear code, message, field, and suggestion guide users to fix errors.

  2. Step 2: Compare options for user-friendliness

    Include error code, message, field name, and suggestion for fix provides detailed, human-readable info; others hide or confuse users.

  3. Final Answer:

    Include error code, message, field name, and suggestion for fix -> Option A

  4. Quick Check:

    Detailed, clear errors improve user experience [OK]
Hint: Add suggestions and field info for clearer error messages [OK]
Common Mistakes:
  • Returning generic messages without guidance
  • Using HTTP 200 for errors causing confusion
  • Hiding error details from users