Stylistic question regarding no-op code and tests

[Peter Otten]

Jason Swails wrote:

> Hi everyone,
> 
> I'd like to get some opinions about some coding constructs that may seem
> at first glance to serve no purpose, but does have *some* non-negligible
> purpose, and I think I've come to the right place :).
> 
> The construct is this:
> 
> def my_function(arg1, arg2, filename=None):
>     """ Some function. If a file is given, it is processed """
>     # Some code that performs my_function
>     if filename is not None:
>         process_file(filename)
>     else:
>         pass
> 
> My question is, what do you think of the "else: pass" statement?  It is a
> complete no-op and is syntactically equivalent to the same code with those
> lines removed.  Up until earlier today, I would look at that and cringe (I
> still do, a little).
> 
> What I recently realized, though, that what this construct allows is for
> the coverage testing package (which I have recently started employing for
> my project... thanks Ned and others!) to detect whether or not both code
> paths are covered in the test suite.
> 
> I think my opinion here is that this construct is useful to use when the
> two code paths are very different operationally from each other, one is an
> unusual path that you are not >100% sure is well-covered in your test
> suite, but that your first instinct should be to avoid such code.
> 
> What do you think?

Rewrite my_function() in such a way that you can devise unit tests that 
verify the process_file path is taken if and only if filename is not None.

The minimal change would be

def my_function(arg1, arg2, filename=None):
    """ Some function. If a file is given, it is processed """
    # Some code that performs my_function
    if filename is not None:
        process_file(filename)
        return True
    else:
        return False

but there are certainly options that better reflect the actual purpose of 
my_function(). coverage.py is a nice addition, but tests are the first line 
of defense against buggy code.