Python and PEP8 - Recommendations on breaking up long lines?

[Steven D'Aprano]

On Wed, 27 Nov 2013 17:57:13 -0800, Victor Hooi wrote:

> Hi,
> 
> I'm running pep8 across my code, and getting warnings about my long
> lines (> 80 characters).
> 
> I'm wonder what's the recommended way to handle the below cases, and fit
> under 80 characters.
> 
> First example - multiple context handlers:
> 
>             with open(self.full_path, 'r') as input,
>             open(self.output_csv, 'ab') as output:


if True:  # add indentation, just for the example's sake.
    if True:
        if True:
            with (open(self.full_path, 'r') as input,
                      open(self.output_csv, 'ab') as output):
                do_this()
                do_that()


 
> Second example - long error messages:
> 
>             self.logger.error('Unable to open input or output file - %s.
>             Please check you have sufficient permissions and the file
>             and parent directory exist.' % e)

Long strings are always ugly :-(

But you can use implicit concatenation to make them a little less so.



if True:  # add indentation, just for the example's sake.
    if True:
        if True:
            self.logger.error(
                'Unable to open input or output file - %s.'
                ' Please check you have sufficient permissions and
                ' the file and parent directory exist.' 
                % e)

Notice that my convention is to use a leading space in the strings when 
doing implicit concatenation, if possible. E.g.:

("Hello"
 " World!")

rather than:

("Hello "
 "World!")


> Third example - long comments:
> 
>             """ NB - We can't use Psycopg2's parametised statements
>             here, as that automatically wraps everything in single
>             quotes. So s3://my_bucket/my_file.csv.gz would become
>             s3://'my_bucket'/'my_file.csv.gz'. Hence, we use Python's
>             normal string formating - this could potentially exposes us
>             to SQL injection attacks via the config.yaml file.
>             I'm not aware of any easy ways around this currently though
>             - I'm open to suggestions though.
>             See
>             http://stackoverflow.com/questions/9354392/psycopg2-cursor-
execute-with-sql-query-parameter-causes-syntax-error
>             for further information. """
> 
> In this case, I'm guessing a using triple quotes (""") is a better idea
> with multi-line comments, right?

*shrug* That's a matter of personal preference.


> However, I've noticed that I can't seem to put in line-breaks inside the
> comment without triggering a warning. For example, trying to put in
> another empty line in between lines 6 and 7 above causes a warning.
> 
> Also, how would I split up the long URLs? Breaking it up makes it
> annoying to use the URL. Thoughts?

I hate long URLs.

There's no good solution to long URLs. Just leave them as they come, and 
if your style checker allows you to flag an exception to the long-line 
rules, use it.


-- 
Steven