Python exception for HTTP response codes

Question

I'd like to raise a Python-standard exception when an HTTP response code from querying an API is not 200, but what specific exception should I use? For now I raise an OSError:

if response.status_code != 200:
  raise OSError("Response " + str(response.status_code)
                  + ": " + response.content)

I'm aware of the documentation for built-in exceptions .

Answer 1

You can simply call Response.raise_for_status() on your response:

>>> import requests
>>> url = 'http://stackoverflow.com/doesnt-exist'
>>> r = requests.get(url)
>>>
>>> print r.status_code
404
>>> r.raise_for_status()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "requests/models.py", line 831, in raise_for_status
    raise HTTPError(http_error_msg, response=self)
requests.exceptions.HTTPError: 404 Client Error: Not Found

This will raise a requests.HTTPError for any 4xx or 5xx response.

See the docs on Response Status Code for a more complete example.

---

Note that this does not exactly do what you asked ( status != 200 ): It will not raise an exception for 201 Created or 204 No Content , or any of the 3xx redirects - but this is most likely the behavior you want: requests will just follow the redirects, and the other 2xx are usually just fine if you're dealing with an API.

Answer 2

The built-in Python exceptions are probably not a good fit for what you are doing. You will want to subclass the base class Exception , and throw your own custom exceptions based on each scenario you want to communicate.

A good example is how the Python Requests HTTP library defines its own exceptions :

In the event of a network problem (eg DNS failure, refused connection, etc), Requests will raise a ConnectionError exception.

In the rare event of an invalid HTTP response, Requests will raise an HTTPError exception.

If a request times out, a Timeout exception is raised.

If a request exceeds the configured number of maximum redirections, a TooManyRedirects exception is raised.

All exceptions that Requests explicitly raises inherit from requests.exceptions.RequestException .