Python and PEP8 - Recommendations on breaking up long lines?

[Victor Hooi]

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:

and in my case, with indents, the 80-character marks is just before the ending "as output".

What's the standard recognised way to split this across multiple lines, so that I'm under 80 characters?

I can't just split after the "as input," as that isn't valid syntax, and there's no convenient parentheses for me to split over.

Is there a standard Pythonic way?

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)

I can use triple quotes:

            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)

However, that will introduce newlines in the message, which I don't want.

I can use backslashes:

            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)

which won't introduce newlines.

Or I can put them all as separate strings, and trust Python to glue them together:

            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)

Which way is the recommended Pythonic way?

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?

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?

Cheers,
Victor