Python and PEP8 - Recommendations on breaking up long lines?

[Roy Smith]

In article <34479463-b8a8-4417-9989-cd29369461c2 at googlegroups.com>,
 Victor Hooi <victorhooi at gmail.com> wrote:

>     cur.executemany("INSERT INTO foobar_foobar_files VALUES (?)",
>                     [[os.path.relpath(filename, foobar_input_folder)] for 
>                     filename in filenames])

I don't often write raw SQL embedded in Python.  I'm much more likely to 
use some sort of ORM layer.  But, if I were doing this, I would break it 
up something like:



There's a few different strategies I employed there.  My first thought 
was a logical break of computing the list of pathnames vs. inserting 
them into the database.  That got me here:

    paths = [[os.path.relpath(filename, foobar_input_folder)] \
      for filename in filenames]
    cur.executemany("INSERT INTO foobar_foobar_files VALUES (?)",
                    paths)

I wouldn't have actually broken the first line with the backslash, but 
I'm doing that to appease my news posting software.

My next step would be some simple textual changes; I'd get rid of the 
overly-line variable names.  In general, I don't like very short 
variable names, but I'm OK with them as long as the scope is very small, 
as it is here:

    paths = [[os.path.relpath(fn, folder)] for fn in filenames]
    cur.executemany("INSERT INTO foobar_foobar_files VALUES (?)",
                    paths)

I'd probably factor out the double lookup of os.path.relpath.  I think 
this is easier to read:

    relpath = os.path.relpath
    paths = [[relpath(fn, folder)] for fn in filenames]
    cur.executemany("INSERT INTO foobar_foobar_files VALUES (?)",
                    paths)

If filenames was a very long list, it would also be a little bit faster 
to execute, but that's such a small factor as to probably be 
unmeasurable.

And, finally, I'd probably move one set of square brackets down into the 
SQL statement.  It really makes more sense there anyway; the bundling up 
of the arguments into a sequence is more a part of the database API than 
it is inherent to the data.

    relpath = os.path.relpath
    paths = [relpath(fn, foobar_input_folder) for fn in filenames]
    cur.executemany("INSERT INTO foobar_foobar_files VALUES (?)",
                    [paths])