how to format long if conditions

Steven D'Aprano steve+comp.lang.python at pearwood.info
Sat Aug 27 09:24:12 CEST 2011


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)

-- 
Steven




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