I'm writing some unit tests where I mock out requests to another service. Here's the method I'm testing.
def ping_camera(self, camera):
retry_ping = Retry(
total=3,
status_forcelist=[404, 429, 500, 502, 503, 504],
method_whitelist=["GET"],
backoff_factor=1,
)
adapter = HTTPAdapter(max_retries=retry_ping)
http = requests.Session()
http.mount("http://", adapter)
try:
response = http.get("http://{}".format(camera.ip_address), timeout=3)
response.raise_for_status()
except Exception as e:
camera.camera_status = False
camera.save()
else:
camera.camera_status = True
camera.save()
And here's one of my tests.
#patch.object(Session, "get")
def test_expects_true_camera_status_to_return_false_status(self, mock):
# Arrange
mock.side_effect = Exception
# Act
check_cams = CheckCameras()
check_cams.ping_camera(self.camera)
# Assert
self.assertFalse(self.camera.camera_status)
Note that in order to have an exception raised, I need to add mock.side_effect = Exception. I come from the Laravel world where only the response status needs to be specified and if a bad response is returned, an exception will be raised.
I can even specify a good response, and still trigger an exception like so
mock.return_value.status_code = 200
mock.side_effect = Exception
Is this just a quirk of a Python testing, or can I have exceptions raised based off the response status code alone?
Meaning if I add mock.return_value.status_code = 500 I'll get an exception raised and hit the except portion of my code block.
I want to test exceptions with Pytest. I send an HTTP request and get a response. I want the response to be corrupt so response.json() goes to the except block. Below are the examples.
Send a request, receive a response:
def send_message_json():
# ...
try:
response = cls.send_message(method, url, **kwargs)
if response:
return response.json() # this is what should fail
except simplejson.errors.JSONDecodeError as err:
raise err # this is to be achieved
The unit test should assert that the simplejson.errors.JSONDecodeError should be raised.
#mock.patch.object(Service, 'send_message_json')
def test_send_message_json_exception(mock_send):
svc = Service()
with pytest.raises(simplejson.errors.JSONDecodeError): # this should assert the exceptions was raised
svc.send_message_json("GET", 'http://my.url/')
I fail to activate the exception raise by the pytest.mock.object. What would make .json() fail in the mock?
I figured it out by mocking the response of the actual request.
In the original question there's send_message_json() method.
It calls send_message() method that returns requests.Response. So I mocked the return value of send_message() that is also a mock instead of send_message_json():
#mock.patch.object(Service, 'send_message') # mock send_message instead
def test_send_message_json_exception(mock_send):
svc = Service()
mocked_response = Response()
mocked_response.status_code = 200
mocked_response.data = '<!doctype html>' # so this is obviously not a JSON
mock_send.return_value = mocked_response # apply the mocked response here
with pytest.raises(simplejson.errors.JSONDecodeError):
svc.send_message_json("GET", 'http://my.url/') # this calls send_message() and returns a bad mocked requests.Response
The bad mocked requests.Response fails at mocked_response.json() in send_message_json() and raises simplejson.errors.JSONDecodeError
try:
response = urllib2.urlopen(request)
except urllib2.URLError as e:
response = json.loads(e.read())
return error(e.code(),response['errors'][0]['message'])
response = json.loads(response.read())
if 'errors' in response:
return error(response['ErrorCode'],response['Error'])
Here is the piece of code I am working with and you can help me out referring to this piece.
e is the caught exception, here an instance of the urllib2.URLError class or a subclass thereof. The code expects that instance to define the e.read() and e.code() methods.
However, it has some errors. It actually assumes it is catching the urllib2.HTTPError exception, a subclass of URLError. The exception handler certainly will catch such exceptions, but it could also be the base URLError, in which case there won't be an e.read() method! It also tries to call HTTPError.code, which is not a method but an attribute.
The HTTPError exception is thrown for HTTP error codes, so only when there was a response from the server. e.read() lets you read the response body from the socket, and e.code is the HTTP code the server responded with. From the documentation:
Though being an exception (a subclass of URLError), an HTTPError can also function as a non-exceptional file-like return value (the same thing that urlopen() returns). This is useful when handling exotic HTTP errors, such as requests for authentication.
For the code to work in all cases, it would have to be corrected to:
try:
response = urllib2.urlopen(request)
except urllib2.HTTPError as e:
response = json.loads(e.read())
return error(e.code, response['errors'][0]['message'])
perhaps with an additional except urllib2.URLError as e: block to handle errors that don't involve a HTTP response.
I've recently started using pytest, and even more recently started using mock for mocking the requests library. I have made a requests.Response object okay, and for a 200 status code it works fine. What I'm trying to do here, is to use raise_for_status() to check for a rate limit exceeded error, and test that it handles the exception with pytest.
I'm using the Mock side_effect option, which seems to fire the exception I'm hoping, but pytest doesn't seem to recognise this as having happened and fails the test.
Any thoughts? I'm sure it's something obvious I'm missing!
The code I have for the class is:
class APIClient:
def get_records(self, url):
try:
r = requests.get(url)
r.raise_for_status()
return r.json()
except requests.HTTPError as e:
print("Handling the exception")
In the test class, I have got:
#pytest.fixture
def http_error_response(rate_limit_json):
mock_response = mock.Mock()
mock_response.json.return_value = rate_limit_json
mock_response.status_code = 429
mock_response.raise_for_status.side_effect = requests.exceptions.HTTPError
return mock_response
class TestRecovery(object):
#mock.patch('requests.get')
def test_throws_exception_for_rate_limit_error\
(self, mock_get, api_query_object, http_error_response):
mock_get.return_value = http_error_response
print(http_error_response.raise_for_status.side_effect)
url = api_query_object.get_next_url()
with pytest.raises(requests.exceptions.HTTPError):
api_query_object.get_records(url)
The output I get is:
with pytest.raises(requests.exceptions.HTTPError):
> api_query_object.get_records(url)
E Failed: DID NOT RAISE
---------------------- Captured stdout call ----------------------
<class 'requests.exceptions.HTTPError'>
Handling the exception
You are instructing pytest to expect an exception that should be raised in APIClient.get_records but inside that method definition you are already capturing the exception and just doing a print.
The exception is actually happening and it proved by seeing the result of your print in the console output.
Instead of that you should either check with the mock that the method raise_for_status was called.
try:
r = requests.get(url, params={'s': thing})
except requests.ConnectionError, e:
print(e)
Is this correct? Is there a better way to structure this? Will this cover all my bases?
Have a look at the Requests exception docs. In short:
In the event of a network problem (e.g. DNS failure, refused connection, etc), Requests will raise a ConnectionError exception.
In the event of the rare 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.
To answer your question, what you show will not cover all of your bases. You'll only catch connection-related errors, not ones that time out.
What to do when you catch the exception is really up to the design of your script/program. Is it acceptable to exit? Can you go on and try again? If the error is catastrophic and you can't go on, then yes, you may abort your program by raising SystemExit (a nice way to both print an error and call sys.exit).
You can either catch the base-class exception, which will handle all cases:
try:
r = requests.get(url, params={'s': thing})
except requests.exceptions.RequestException as e: # This is the correct syntax
raise SystemExit(e)
Or you can catch them separately and do different things.
try:
r = requests.get(url, params={'s': thing})
except requests.exceptions.Timeout:
# Maybe set up for a retry, or continue in a retry loop
except requests.exceptions.TooManyRedirects:
# Tell the user their URL was bad and try a different one
except requests.exceptions.RequestException as e:
# catastrophic error. bail.
raise SystemExit(e)
As Christian pointed out:
If you want http errors (e.g. 401 Unauthorized) to raise exceptions, you can call Response.raise_for_status. That will raise an HTTPError, if the response was an http error.
An example:
try:
r = requests.get('http://www.google.com/nothere')
r.raise_for_status()
except requests.exceptions.HTTPError as err:
raise SystemExit(err)
Will print:
404 Client Error: Not Found for url: http://www.google.com/nothere
One additional suggestion to be explicit. It seems best to go from specific to general down the stack of errors to get the desired error to be caught, so the specific ones don't get masked by the general one.
url='http://www.google.com/blahblah'
try:
r = requests.get(url,timeout=3)
r.raise_for_status()
except requests.exceptions.HTTPError as errh:
print ("Http Error:",errh)
except requests.exceptions.ConnectionError as errc:
print ("Error Connecting:",errc)
except requests.exceptions.Timeout as errt:
print ("Timeout Error:",errt)
except requests.exceptions.RequestException as err:
print ("OOps: Something Else",err)
Http Error: 404 Client Error: Not Found for url: http://www.google.com/blahblah
vs
url='http://www.google.com/blahblah'
try:
r = requests.get(url,timeout=3)
r.raise_for_status()
except requests.exceptions.RequestException as err:
print ("OOps: Something Else",err)
except requests.exceptions.HTTPError as errh:
print ("Http Error:",errh)
except requests.exceptions.ConnectionError as errc:
print ("Error Connecting:",errc)
except requests.exceptions.Timeout as errt:
print ("Timeout Error:",errt)
OOps: Something Else 404 Client Error: Not Found for url: http://www.google.com/blahblah
Exception object also contains original response e.response, that could be useful if need to see error body in response from the server. For example:
try:
r = requests.post('somerestapi.com/post-here', data={'birthday': '9/9/3999'})
r.raise_for_status()
except requests.exceptions.HTTPError as e:
print (e.response.text)
Here's a generic way to do things which at least means that you don't have to surround each and every requests call with try ... except:
Basic version
# see the docs: if you set no timeout the call never times out! A tuple means "max
# connect time" and "max read time"
DEFAULT_REQUESTS_TIMEOUT = (5, 15) # for example
def log_exception(e, verb, url, kwargs):
# the reason for making this a separate function will become apparent
raw_tb = traceback.extract_stack()
if 'data' in kwargs and len(kwargs['data']) > 500: # anticipate giant data string
kwargs['data'] = f'{kwargs["data"][:500]}...'
msg = f'BaseException raised: {e.__class__.__module__}.{e.__class__.__qualname__}: {e}\n' \
+ f'verb {verb}, url {url}, kwargs {kwargs}\n\n' \
+ 'Stack trace:\n' + ''.join(traceback.format_list(raw_tb[:-2]))
logger.error(msg)
def requests_call(verb, url, **kwargs):
response = None
exception = None
try:
if 'timeout' not in kwargs:
kwargs['timeout'] = DEFAULT_REQUESTS_TIMEOUT
response = requests.request(verb, url, **kwargs)
except BaseException as e:
log_exception(e, verb, url, kwargs)
exception = e
return (response, exception)
NB
Be aware of ConnectionError which is a builtin, nothing to do with the class requests.ConnectionError*. I assume the latter is more common in this context but have no real idea...
When examining a non-None returned exception, requests.RequestException, the superclass of all the requests exceptions (including requests.ConnectionError), is not "requests.exceptions.RequestException" according to the docs. Maybe it has changed since the accepted answer.**
Obviously this assumes a logger has been configured. Calling logger.exception in the except block might seem a good idea but that would only give the stack within this method! Instead, get the trace leading up to the call to this method. Then log (with details of the exception, and of the call which caused the problem)
*I looked at the source code: requests.ConnectionError subclasses the single class requests.RequestException, which subclasses the single class IOError (builtin)
**However at the bottom of this page you find "requests.exceptions.RequestException" at the time of writing (2022-02)... but it links to the above page: confusing.
Usage is very simple:
search_response, exception = utilities.requests_call('get',
f'http://localhost:9200/my_index/_search?q={search_string}')
First you check the response: if it's None something funny has happened and you will have an exception which has to be acted on in some way depending on context (and on the exception). In Gui applications (PyQt5) I usually implement a "visual log" to give some output to the user (and also log simultaneously to the log file), but messages added there should be non-technical. So something like this might typically follow:
if search_response == None:
# you might check here for (e.g.) a requests.Timeout, tailoring the message
# accordingly, as the kind of error anyone might be expected to understand
msg = f'No response searching on |{search_string}|. See log'
MainWindow.the().visual_log(msg, log_level=logging.ERROR)
return
response_json = search_response.json()
if search_response.status_code != 200: # NB 201 ("created") may be acceptable sometimes...
msg = f'Bad response searching on |{search_string}|. See log'
MainWindow.the().visual_log(msg, log_level=logging.ERROR)
# usually response_json will give full details about the problem
log_msg = f'search on |{search_string}| bad response\n{json.dumps(response_json, indent=4)}'
logger.error(log_msg)
return
# now examine the keys and values in response_json: these may of course
# indicate an error of some kind even though the response returned OK (status 200)...
Given that the stack trace is logged automatically you often need no more than that...
Advanced version when json object returned
(... potentially sparing a great deal of boilerplate!)
To cross the Ts, when a json object is expected to be returned:
If, as above, an exception gives your non-technical user a message "No response", and a non-200 status "Bad response", I suggest that
a missing expected key in the response's JSON structure should give rise to a message "Anomalous response"
an out-of-range or strange value to a message "Unexpected response"
and the presence of a key such as "error" or "errors", with value True or whatever, to a message "Error response"
These may or may not prevent the code from continuing.
... and in fact to my mind it is worth making the process even more generic. These next functions, for me, typically cut down 20 lines of code using the above requests_call to about 3, and make most of your handling and your log messages standardised. More than a handful of requests calls in your project and the code gets a lot nicer and less bloated:
def log_response_error(response_type, call_name, deliverable, verb, url, **kwargs):
# NB this function can also be used independently
if response_type == 'No': # exception was raised (and logged)
if isinstance(deliverable, requests.Timeout):
MainWindow.the().visual_log(f'Time out of {call_name} before response received!', logging.ERROR)
return
else:
if isinstance(deliverable, BaseException):
# NB if response.json() raises an exception we end up here
log_exception(deliverable, verb, url, kwargs)
else:
# if we get here no exception has been raised, so no stack trace has yet been logged.
# a response has been returned, but is either "Bad" or "Anomalous"
response_json = deliverable.json()
raw_tb = traceback.extract_stack()
if 'data' in kwargs and len(kwargs['data']) > 500: # anticipate giant data string
kwargs['data'] = f'{kwargs["data"][:500]}...'
added_message = ''
if hasattr(deliverable, 'added_message'):
added_message = deliverable.added_message + '\n'
del deliverable.added_message
call_and_response_details = f'{response_type} response\n{added_message}' \
+ f'verb {verb}, url {url}, kwargs {kwargs}\nresponse:\n{json.dumps(response_json, indent=4)}'
logger.error(f'{call_and_response_details}\nStack trace: {"".join(traceback.format_list(raw_tb[:-1]))}')
MainWindow.the().visual_log(f'{response_type} response {call_name}. See log.', logging.ERROR)
def check_keys(req_dict_structure, response_dict_structure, response):
# so this function is about checking the keys in the returned json object...
# NB both structures MUST be dicts
if not isinstance(req_dict_structure, dict):
response.added_message = f'req_dict_structure not dict: {type(req_dict_structure)}\n'
return False
if not isinstance(response_dict_structure, dict):
response.added_message = f'response_dict_structure not dict: {type(response_dict_structure)}\n'
return False
for dict_key in req_dict_structure.keys():
if dict_key not in response_dict_structure:
response.added_message = f'key |{dict_key}| missing\n'
return False
req_value = req_dict_structure[dict_key]
response_value = response_dict_structure[dict_key]
if isinstance(req_value, dict):
# if the response at this point is a list apply the req_value dict to each element:
# failure in just one such element leads to "Anomalous response"...
if isinstance(response_value, list):
for resp_list_element in response_value:
if not check_keys(req_value, resp_list_element, response):
return False
elif not check_keys(req_value, response_value, response): # any other response value must be a dict (tested in next level of recursion)
return False
elif isinstance(req_value, list):
if not isinstance(response_value, list): # if the req_value is a list the reponse must be one
response.added_message = f'key |{dict_key}| not list: {type(response_value)}\n'
return False
# it is OK for the value to be a list, but these must be strings (keys) or dicts
for req_list_element, resp_list_element in zip(req_value, response_value):
if isinstance(req_list_element, dict):
if not check_keys(req_list_element, resp_list_element, response):
return False
if not isinstance(req_list_element, str):
response.added_message = f'req_list_element not string: {type(req_list_element)}\n'
return False
if req_list_element not in response_value:
response.added_message = f'key |{req_list_element}| missing from response list\n'
return False
# put None as a dummy value (otherwise something like {'my_key'} will be seen as a set, not a dict
elif req_value != None:
response.added_message = f'required value of key |{dict_key}| must be None (dummy), dict or list: {type(req_value)}\n'
return False
return True
def process_json_requests_call(verb, url, **kwargs):
# "call_name" is a mandatory kwarg
if 'call_name' not in kwargs:
raise Exception('kwarg "call_name" not supplied!')
call_name = kwargs['call_name']
del kwargs['call_name']
required_keys = {}
if 'required_keys' in kwargs:
required_keys = kwargs['required_keys']
del kwargs['required_keys']
acceptable_statuses = [200]
if 'acceptable_statuses' in kwargs:
acceptable_statuses = kwargs['acceptable_statuses']
del kwargs['acceptable_statuses']
exception_handler = log_response_error
if 'exception_handler' in kwargs:
exception_handler = kwargs['exception_handler']
del kwargs['exception_handler']
response, exception = requests_call(verb, url, **kwargs)
if response == None:
exception_handler('No', call_name, exception, verb, url, **kwargs)
return (False, exception)
try:
response_json = response.json()
except BaseException as e:
logger.error(f'response.status_code {response.status_code} but calling json() raised exception')
# an exception raised at this point can't truthfully lead to a "No response" message... so say "bad"
exception_handler('Bad', call_name, e, verb, url, **kwargs)
return (False, response)
status_ok = response.status_code in acceptable_statuses
if not status_ok:
response.added_message = f'status code was {response.status_code}'
log_response_error('Bad', call_name, response, verb, url, **kwargs)
return (False, response)
check_result = check_keys(required_keys, response_json, response)
if not check_result:
log_response_error('Anomalous', call_name, response, verb, url, **kwargs)
return (check_result, response)
Example call (NB with this version, the "deliverable" is either an exception or a response which delivers a json structure):
success, deliverable = utilities.process_json_requests_call('get',
f'{ES_URL}{INDEX_NAME}/_doc/1',
call_name=f'checking index {INDEX_NAME}',
required_keys={'_source':{'status_text': None}})
if not success: return False
# here, we know the deliverable is a response, not an exception
# we also don't need to check for the keys being present:
# the generic code has checked that all expected keys are present
index_status = deliverable.json()['_source']['status_text']
if index_status != 'successfully completed':
# ... i.e. an example of a 200 response, but an error nonetheless
msg = f'Error response: ES index {INDEX_NAME} does not seem to have been built OK: cannot search'
MainWindow.the().visual_log(msg)
logger.error(f'index |{INDEX_NAME}|: deliverable.json() {json.dumps(deliverable.json(), indent=4)}')
return False
So the "visual log" message seen by the user in the case of missing key "status_text", for example, would be "Anomalous response checking index XYZ. See log." (and the log would give a more detailed technical message, constructed automatically, including the stack trace but also details of the missing key in question).
NB
mandatory kwarg: call_name; optional kwargs: required_keys, acceptable_statuses, exception_handler.
the required_keys dict can be nested to any depth
finer-grained exception-handling can be accomplished by including a function exception_handler in kwargs (though don't forget that requests_call will have logged the call details, the exception type and __str__, and the stack trace).
in the above I also implement a check on key "data" in any kwargs which may be logged. This is because a bulk operation (e.g. to populate an index in the case of Elasticsearch) can consist of enormous strings. So curtail to the first 500 characters, for example.
PS Yes, I do know about the elasticsearch Python module (a "thin wrapper" around requests). All the above is for illustration purposes.