Python: Use return value to find reason for an error

Question

The python module that am using has list of error codes like the following: -

DRV_ERROR_CODES = 20001
DRV_SUCCESS = 20002
DRV_VXDNOTINSTALLED = 20003
DRV_ERROR_SCAN = 20004
DRV_ERROR_CHECK_SUM = 20005
DRV_ERROR_FILELOAD = 20006
DRV_UNKNOWN_FUNCTION = 20007
...

I currently just compare the return value against the success error code in order check if the process has been successful.

if atmcd.DRV_SUCCESS==ret:

I would like to use the return value and output what exactly caused the error (e.g. the return value was 2004, therefore the script will print that there was a scan error). Is there a a way to compare against all these variables? Is there a better way of finding the error?

@adsmith: presumably the module already uses *one* exception, with an error code on it. — Martijn Pieters, Dec 18 '13 at 16:38
I don't really have control of the module. It's a python wrapper on top of an SDK written in C++. These are the error codes coming out of SDK. — Marmstrong, Dec 18 '13 at 16:38

Martijn Pieters · Accepted Answer · 2013-12-18T16:44:17.143

6

You can collect all error codes in a mapping:

errornames = {value: name for name, value in vars(atmcd).items() if name.isupper() and name.startswith('DRV_')}

This produces a mapping from error code to name used in the atmcd module:

{'20007': 'DRV_UNKNOWN_FUNCTION', '20006': 'DRV_ERROR_FILELOAD', '20005': 'DRV_ERROR_CHECK_SUM', '20004': 'DRV_ERROR_SCAN', '20003': 'DRV_VXDNOTINSTALLED', '20002': 'DRV_SUCCESS', '20001': 'DRV_ERROR_CODES'}

Now you can both test for the error code and get the name for each:

if ret in errornames:
    print 'Received a {} code'.format(errornames[ret])

edited Dec 18 '13 at 16:44

answered Dec 18 '13 at 16:37

Martijn Pieters

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Missing an `.items()`, I think. Fix that and since you beat me I can delete mine. – DSM Dec 18 '13 at 16:43
@DSM: I could have sworn I had that in there.. Thanks for the pointer. – Martijn Pieters Dec 18 '13 at 16:44
I new about dictionaries but that first line of code is amazing. Its exactly what I need. I have learned a lot of different things from this answer that will help me elsewhere. Thanks – Marmstrong Dec 18 '13 at 17:18

score 1 · Answer 2 · answered Dec 18 '13 at 16:38

This is an arcane way of programming. Modern programming languages use Exceptions to inform of errors. If I were you I would group all the variables in a dict this way: {error_code:'error_name'} and write a wrapper for the method that do this:

ret = method_call()
if ret != atmcd.DRV_SUCCESS:
    raise Exception('Error number %d: %s' % (error_code, error_name))

Maybe a good way doing this is with a decorator to the actual method you're calling.

Hope this helps!

score 0 · Answer 3 · answered Dec 18 '13 at 16:43

You can use a dictionary which maps the error code with the string to be printed

errors = { DRV_ERROR_CODES : 'Explanation for this error code',
           DRV_SUCCESS : 'Explanation for this error code',
           DRV_VXDNOTINSTALLED : 'Explanation for this error code',
           DRV_ERROR_SCAN : 'Explanation for this error code',
           DRV_ERROR_CHECK_SUM : 'Explanation for this error code',
           DRV_ERROR_FILELOAD : 'Explanation for this error code',
           DRV_UNKNOWN_FUNCTION : 'Explanation for this error code'}

if ret in errors.keys():
    print errors[ret]

OP mentioned there are over 100 of these error codes. a hand-written Dictionary would be a Bad Idea. — Adam Smith, Dec 18 '13 at 16:55

score 0 · Answer 4 · answered Dec 18 '13 at 17:19

def error_track(code):

    return {
            20001: "ERROR",
            20002: "SUCCESS",
            20003: "FILE LOAD ERROR",
            20004: "ERROR CHECK SUm"
            }.get(code, "UNKNOWN ERROR")


print error_track(20001)
print error_track(50000)

OUTPUT

ERROR
UNKNOWN ERROR

Python: Use return value to find reason for an error

4 Answers4