[TIP] Test runner checking for absence of 'None' in all functions (pytest)

[David]

Hi Ned,

thanks for the guidance -- this is very helpful indeed!

David


On 24/01/16 01:59, Ned Batchelder wrote:
> On 1/23/16 4:27 PM, David wrote:
>> Dear fellow Pythonistas,
>>
>> I am currently reading a book [1] that gives the following coding tip:
>> "Prefer    Exceptions to Returning    None". You can see code examples
>> out of
>> the book further below.
>>
>> As I am teaching myself pytest these days, I would like to write a test
>> runner (which eventually is to be part of a Continuous Integration
>> setup) that fails should it detect any function that returns None.
> This sounds like a job for pyflakes or pylint, not a test runner.
> Especially because a function with no return statement at all will
> return None. It sounds like you want to find explicit "return None"
> statements.  Static analysis such as pylint does sounds right for this job.
> 
> --Ned.
>> My problem is that I would like to limit the test runner to look
>> *inside* of functions (and/or other structures).
>>
>> I can very well write a parser that checks, per line, if the words
>> "return" and "None" are used. But that would cover the entire file in
>> question, never mind its structure.
>>
>> Do you have any ideas how to check the 'absence of None' within
>> functions and the like?
>>
>> I am looking forward to your suggestions!
>>
>> Greetings and thanks,
>>
>> David
>>
>>
>>
>>
>> # bad code
>> def divide(a, b):
>>      try:
>>          return a / b
>>      except ZeroDivisionError:
>>     return None
>>
>>
>> # good code
>> def divide(a, b):
>>      try:
>>     return a / b
>>      except ZeroDivisionError as e:
>>     raise ValueError(‘Invalid inputs’) from    e
>>
>>
>> [1] Brett Slatkin (2015), Effective Python, Addison-Wesley
>>
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> 
> 
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