Python requests library Exception handling

Question

I am creating a download service using the python requests library (See here) to download data from another server. The problem is that sometimes I get a 503 error and I need to display an appropriate message. See sample code below:

import requests
s = requests.Session()
response = s.get('http://mycustomserver.org/download')

I can check from response.status_code and get the status code = 200. But how do I try/catch for a specific error, in this case, I want to be able to detect 503 error and handle them appropriately.

How do I do that?

Solution 1

Why not do

class MyException(Exception);
   def __init__(self, error_code, error_msg):
       self.error_code = error_code
       self.error_msg = error_msg

import requests
s = requests.Session()
response = s.get('http://mycustomserver.org/download')

if response.status_code == 503:
    raise MyException(503, "503 error code")

Edit:

It seems that requests library will also raise an Exception for you using response.raise_for_status()

>>> import requests
>>> requests.get('https://google.com/admin')
<Response [404]>
>>> response = requests.get('https://google.com/admin')
>>> response.raise_for_status()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/requests/models.py", line 638, in raise_for_status
    raise http_error
requests.exceptions.HTTPError: 404 Client Error: Not Found

Edit2:

Wrap you raise_for_status with the following try/except

try:
    if response.status_code == 503:
        response.raise_for_status()
except requests.exceptions.HTTPError as e: 
    if e.response.status_code == 503:
        #handle your 503 specific error

Solution 2

You might as well do this:

try:
    s = requests.Session()
    response = requests.get('http://mycustomserver.org/download')
    if response.status_code == 503:
        response.raise_for_status()
except requests.exceptions.HTTPError:
    print "oops something unexpected happened!"

response.raise_for_status() raises a requests.exceptions.HTTPError and here we are only calling response.raise_for_status() if the status code is equal to 503

Comments

[Frankline]

I was looking at Errors and Exceptions part and wondering which will enable me to catch the 503 error. Thanks though.

[Martin Konecny]

I see - added the relevant try/except block.

[Stryker]

@MartinKonecny - How do you check for all errors instead of listing each one by one. ? i.e. http error, bad url error, ssl certificate error, etc.... is there a general exception handler that cover all errors? Or I am just going about this in the wrong way?

[Martin Konecny]

@Stryker You could can catch all exceptions using except e: and then over time put in multiple more specific catches to have a unique behaviour for each situation (if you need that of course)