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

```