On 27 August 2011 08:24, Steven D'Aprano
<steve+comp.lang.pyt...@pearwood.info> wrote:
> Arnaud Delobelle wrote:
>
>> Hi all,
>>
>> I'm wondering what advice you have about formatting if statements with
>> long conditions (I always format my code to <80 colums)
>>
>> Here's an example taken from something I'm writing at the moment and
>> how I've formatted it:
>>
>>
>> if (isinstance(left, PyCompare) and isinstance(right, PyCompare)
>> and left.complist[-1] is right.complist[0]):
>> py_and = PyCompare(left.complist + right.complist[1:])
>> else:
>> py_and = PyBooleanAnd(left, right)
>>
>> What would you do?
>
> I believe that PEP 8 now suggests something like this:
>
> if (
> isinstance(left, PyCompare) and isinstance(right, PyCompare)
> and left.complist[-1] is right.complist[0]):
> )
> py_and = PyCompare(left.complist + right.complist[1:]
> else:
> py_and = PyBooleanAnd(left, right)
>
>
> I consider that hideous and would prefer to write this:
>
>
> if (isinstance(left, PyCompare) and isinstance(right, PyCompare)
> and left.complist[-1] is right.complist[0]):
> py_and = PyCompare(left.complist + right.complist[1:]
> else:
> py_and = PyBooleanAnd(left, right)
>
>
> Or even this:
>
> tmp = (
> isinstance(left, PyCompare) and isinstance(right, PyCompare)
> and left.complist[-1] is right.complist[0])
> )
> if tmp:
> py_and = PyCompare(left.complist + right.complist[1:]
> else:
> py_and = PyBooleanAnd(left, right)
>
>
> But perhaps the best solution is to define a helper function:
>
> def is_next(left, right):
> """Returns True if right is the next PyCompare to left."""
> return (isinstance(left, PyCompare) and isinstance(right, PyCompare)
> and left.complist[-1] is right.complist[0])
> # PEP 8 version left as an exercise.
>
>
> # later...
> if is_next(left, right):
> py_and = PyCompare(left.complist + right.complist[1:]
> else:
> py_and = PyBooleanAnd(left, right)
>
Thanks Steven and Hans for you suggestions. For this particular
instance I've decided to go for a hybrid approach:
* Add two methods to PyCompare:
class PyCompare(PyExpr):
...
def extends(self, other):
if not isinstance(other, PyCompare):
return False
else:
return self.complist[0] == other.complist[-1]
def chain(self, other):
return PyCompare(self.complist + other.complist[1:])
* Rewrite the if as:
if isinstance(right, PyCompare) and right.extends(left):
py_and = left.chain(right)
else:
py_and = PyBooleanAnd(left, right)
The additional benefit is to hide the implementation details of
PyCompare (I suppose this could illustrate the thread on when to
create functions).
--
Arnaud
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