← VCE Software Development U4O1

Handling API errors

Check a response's status code (200 OK, 404 not found) and wrap requests.get() in try/except so a failed API call shows a friendly message, not a crash.

Part of: VCE Software Development - U4O1 - development and evaluation — Module 124, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 112, QCE Digital Solutions Unit 4 — Prototype Digital Data Exchanges — Module 93

Understanding Handling API errors in VCE Software Development U4O1

What it does: This branch tests for the 404 not found code, so the program can show a message instead of using data that does not exist. The call that might fail goes inside try, so if it raises an exception the except block runs and the program keeps going. 200 means OK: the server found the data and sent it back. 404 means the resource was not found. Use == to compare. A single = is assignment and causes a syntax error in an if statement. A friendly message is clear and tells the user what to do. Raw error text confuses users and is poor feedback.

Common mistakes: A single = assigns a value and is a syntax error in an if condition. Use == to compare the status code with 200. The except line must end with a colon. It should be except requests.Timeout:.

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This module's key terms are also in a printable crossword (Modules 115–124) and word search (Modules 115–171).

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Learning

Duo

Which status code means an API request worked?

404200

Matches

if response.status_code = 200:

↓

A single = assigns a value, so it is a syntax error. Use == to compare the status code with 200.

Applying

Meanings

Term

response.status_code

Meaning

Check a response's status code (200 OK, 404 not found) and wrap requests.get() in try/except so a failed API call shows a friendly message, not a crash.

Practice

import requests

Testing

Gaps

if response. == 200:

Check Answer

Spots

3r = requests.get(url)

4if r.status_code = 200:

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Quick Questions

1. Which status code means an API request worked?

A. 200 ✓

B. 404

200 means OK: the server found the data and sent it back. 404 means the resource was not found.

2. Which line checks whether the request succeeded?

A. if response.status_code = 200:

B. if response.status_code == 200: ✓

Use == to compare. A single = is assignment and causes a syntax error in an if statement.

3. What does a status code of 404 tell your program?

A. The requested resource was not found ✓

B. The request worked and the data is ready

404 means not found, for example a wrong URL or ID. Check the code before reading the data.

4. Which code stops the program from crashing if the internet connection drops?

A. response = requests.get(url) print("Could not connect")

B. try: response = requests.get(url) except requests.exceptions.RequestException: print("Could not connect") ✓

A failed connection raises an exception. Only try/except can catch it so the program keeps running.

5. Which message is better for a user when the API call fails?

A. Sorry, we could not load the data. Please try again. ✓

B. requests.exceptions.ConnectionError: HTTPSConnectionPool

A friendly message is clear and tells the user what to do. Raw error text confuses users and is poor feedback.

Match the Pairs

response.status_code == 200 → Checks whether the API call succeeded, because status code 200 means OK and the data came back.

except requests.exceptions.RequestException: → Catches a failed API call, such as no internet or a timeout, so the program can show a friendly message instead of crashing.

A 404 status code means the resource was not found, so the program should tell the user rather than read the data. → elif response.status_code == 404:

Wrap requests.get() in a try block so that a connection failure can be handled by an except block. → try: response = requests.get(url)

if response.status_code = 200: → A single = assigns a value, so it is a syntax error. Use == to compare the status code with 200.

response = requests.get(url) print(response.json()) → The call is not in try/except and the status is not checked, so a failed call crashes the program or gives bad data.

Key Term

response.status_code

Check a response's status code (200 OK, 404 not found) and wrap requests.get() in try/except so a failed API call shows a friendly message, not a crash.

Fill in the Blanks

1. if response.status_code == 200:

Hint: Type the response attribute that holds the number showing whether the request worked.

2. try: response = requests.get(url) except requests.exceptions.RequestException:

Hint: Type the keyword that starts the block of code which might fail.

3. response = requests.get(url) if response.status_code == 404: print("Not found")

Hint: Type the variable name that holds the result of the API call.

4. try: r = requests.get(url, timeout=5) except requests.exceptions.RequestException:

Hint: Type the base exception class that catches any error raised by the requests library.

5. except requests.exceptions.RequestException: print("Could not connect.")

Hint: Type the function that shows the user a friendly message instead of crashing.

Spot the Error

Question 1

A import requests

B url = 'https://x.com/api'

C r = requests.get(url)

D if r.status_code = 200:

E print('Success')

Line D — A single = assigns a value and is a syntax error in an if condition. Use == to compare the status code with 200.

Question 2

A try:

B r = requests.get(url)

C except requests.Timeout

D print('Server too slow')

Line C — The except line must end with a colon. It should be except requests.Timeout:

Question 3

A r = requests.get(url)

B if r.status_code == '404':

C print('Not found')

D else:

E print(r.json())

Line B — status_code is an integer, so comparing it with the string '404' is never true. It should be == 404 with no quotes.

Question 4

A import request

B try:

C r = requests.get(url)

D except requests.Timeout:

E print('Try again later')

Line A — The library is called requests, with an s. Importing request fails with a ModuleNotFoundError.

Question 5

A r = requests.get(url)

B if r.status_code == 200:

C data = r.json

D else:

E print('Failed')

Line C — Without brackets, data holds the json method instead of the response data. It should be r.json() to call the method.

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