pylint -- should I just ignore it sometimes?

Jean-Michel Pichavant jeanmichel at sequans.com
Thu Oct 21 11:27:57 CEST 2010


Steven D'Aprano wrote:
> On Wed, 20 Oct 2010 12:47:02 +0200, Jean-Michel Pichavant wrote:
>
>   
>> except ValueError, e:
>>
>> Use meaningful names, this is so important. 'e' is not meaningful.
>> 'exception' would be slighly better.
>>     
>
> While I agree with everything else you had to say, I have to take 
> exception to this comment [pun intended].
>
> "e" as a short name for a generic exception instance is perfectly 
> reasonable, like:
>
> i, j, k for an index, or a loop variable
>     e.g. for i in range(100)
> n for some other integer variable
> s for a string
> x for a float, or an arbitrary sequence object
>     e.g. [x.spam() for x in some_sequence]
>
> and similar.
>
> The last example is very instructive. What do you gain by racking your 
> brain for a "more meaningful" name instead of x? The obvious 
> alternatives, "obj" or "item", are equally generic as "x", they don't add 
> any further information. And how much information do you need? It's easy 
> to parody:
>
> [some_sequence_item.spam() for some_sequence_item in some_sequence]
>
> The very shortness of the name is valuable because it reduces the *human* 
> parsing time in reading, and there is no cost because the conventions are 
> so familiar. The convention of "for i in ..." says "this is a loop over 
> an integer" so strongly, that I would argue that "for index in ..." would 
> actually *delay* comprehension.
>
> Furthermore, the use of a single letter cues the reader that this 
> variable isn't notable -- there's nothing unusual or unconventional about 
> it, or it isn't the important part of the algorithm, or that its scope is 
> severely limited. For instance, consider the classic example of 
> exchanging two variables in Python:
>
> a, b = b, a
>
> versus:
>
> thing, other_thing = other_thing, thing
>
> The first example puts the emphasis on the *technique*, not the 
> variables. The second obscures it behind needlessly longer but still 
> generic names.
>
> You are absolutely right to insist on meaningful variable names. Where 
> you go wrong is to assume that single letter names can't be meaningful.
>
>
>   

You are using meaningless example without any context, for sure you 
won't find a proper meaningful name.
Let me quote the paper I linked in the previous post:

list1 = []
for x in theList:
    if x[0] == 4: 
        list1 += x;
return list1

compare it to:

flaggedCells = []
for cell in theBoard:
    if cell[STATUS_VALUE] == FLAGGED:
        flaggedCells += cell
return flaggedCells   

There is another important point: the time where code size matters is over. Now we have the opportunity to write better structured english and that is priceless. Why to your opinion Python has the 'not in' operator ?.
Code is written once, but read dozen of times so we should pay attention to how it reads, not really how long it takes to write. You won't be that happy everyone wrote their mail in this list like a mobile text message, if u c what I mean.

JM





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