chembl_webresource_client - RetryError Exception

Molecule Tutorials - Herong's Tutorial Examples

∟ChEMBL Database - European Molecular Biology Laboratory

∟chembl_webresource_client - RetryError Exception

This section provides a tutorial example to demonstrate a design issue in chembl_webresource_client, where the HTTP Status Code of '404 (Not Found)' is not handled properly.

chembl_webresource_client has a small design issue in its RetryError Exception. If you try to get a data entity with bad ID code, chembl_webresource_client will perform multiple retry requests, even the first request already returns a HTTP Status Code of "404 (Not Found)".

Below is a sample session that shows this problem:

herong$ python3

>>> from chembl_webresource_client.new_client import new_client
>>> molecule = new_client.molecule.get('JUNK')

Traceback (most recent call last):
  ...
  ".../python3.7/site-packages/urllib3/util/retry.py", line 574, in 
  increment raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='www.ebi.ac.uk',
  port=443): Max retries exceeded with url: /chembl/api/data/molecule/JUNK
  (Caused by ResponseError('too many 404 error responses'))

During handling of the above exception, another exception occurred:
Traceback (most recent call last):
  ...
  ".../python3.7/site-packages/requests/adapters.py", line 507, in send
    raise RetryError(e, request=request)
requests.exceptions.RetryError: HTTPSConnectionPool(host='www.ebi.ac.uk',
  port=443): Max retries exceeded with url: /chembl/api/data/molecule/JUNK
  (Caused by ResponseError('too many 404 error responses'))

If you run a HTTP request directly with the "curl" command, you will see the "HTTP/1.1 404 Not Found" message in the response header.

herong$ curl -D h.txt https://www.ebi.ac.uk/chembl/api/data/molecule/JUNK

herong$ more h.txt 

HTTP/1.1 404 Not Found
Server: gunicorn/20.0.4
Vary: Accept, Origin
Content-Type: text/html; charset=utf-8
Strict-Transport-Security: max-age=0
Connection: Keep-Alive
Content-Length: 0