How do you protect yourself from missing comma in vertical string list in python?

Question

In python, it's common to have vertically-oriented lists of string. For example:

subprocess.check_output( [
  'application',
  '-first-flag',
  '-second-flag',
  '-some-additional-flag'
] )

This looks good, readable, don't violate 80-columns rule... But if comma is missed, like this:

subprocess.check_output( [
  'application',
  '-first-flag'  # missed comma here
  '-second-flag',
  '-some-additional-flag'
] )

Python will still assume this code valid by concatenating two stings :(. Is it possible to somehow safeguard yourself from such typos while still using vertically-oriented string lists and without bloating code (like enveloping each items inside str())?

Answer 1

You can have commas at the end of a line after whitespace, like this:

subprocess.check_output( [
   'application'           ,
   '-first-flag'           ,
   '-second-flag'          ,
   '-some-additional-flag' ,
] )

Doing it that way looks a little worse, but it is easy to spot if you have missed any arguments.

Answer 2

You could wrap each string in parens:

subprocess.check_output( [
  ('application'),
  ('-first-flag'),
  ('-second-flag'),
  ('-some-additional-flag'),
] )

And btw, Python is fine with a trailing comma, so just always use a comma at the end of the line, that should also reduce errors.