Multi-line function calls with strings in python

Question

I have a function call in python 2.7:

execute_cmd('/sbin/ip addr flush dev '
             + args.interface
             + ' && '
             + '/sbin/ifdown '
             + args.interface
             + ' ; '
             + '/sbin/ifup '
             + args.interface
             + ' && '
             + '/sbin/ifconfig | grep '
             + args.interface)

This is running fine, but pylint is complaining with the following warning messages:

C:220, 0: Wrong continued indentation (remove 1 space).
                    + args.interface
                   |^ (bad-continuation)
C:221, 0: Wrong continued indentation (remove 1 space).
                    + ' && '
                   |^ (bad-continuation)
C:222, 0: Wrong continued indentation (remove 1 space).
                    + '/sbin/ifconfig | grep '
                   |^ (bad-continuation)
.
.
.

What is the correct way to call a function in python with string argument(s) which spans across multiple lines?.

It is once you apply the [most important rule in PEP8](https://www.python.org/dev/peps/pep-0008/#a-foolish-consistency-is-the-hobgoblin-of-little-minds). — timgeb, Dec 15 '17 at 09:32
Why not format the string before passing it to the function? Solves your problem and is much better readable. — meow, Dec 15 '17 at 09:35
Yes, will pass the string after forming it properly instead of forming it during the function call. Good one. — Vijay47, Dec 15 '17 at 09:40

Mel · Answer 1 · 2017-12-15T09:38:34.993

1

Pylint tells you exactly what to do, remove one space:

execute_cmd('/sbin/ip addr flush dev '
            + args.interface
            + ' && '
            + '/sbin/ifdown '
            + args.interface
            + ' ; '
            + '/sbin/ifup '
            + args.interface
            + ' && '
            + '/sbin/ifconfig | grep '
            + args.interface)

Also, you could use string formatting, for example:

command_line = '/sbin/ip addr flush dev {0} && /sbin/ifdown {0} ; /sbin/ifup {0} && {0} /sbin/ifconfig | grep {0}'\
    .format(args.interface)

edited Dec 15 '17 at 09:38

answered Dec 15 '17 at 09:32

Mel

5,837
10
37
42

I am using atom IDE. When I try to remove 1 space, its removing 4. – Vijay47 Dec 15 '17 at 09:37
Well that's a different question: 'How to make atom IDE indent python properly ?' You should ask a new question. – Mel Dec 15 '17 at 09:41
The second code may span more than 80 characters which breaks the pep8 rule. – Vijay47 Dec 15 '17 at 09:41

Arne · Answer 2 · 2017-12-15T10:11:24.913

PEP 8 states that you can also start a long argument list (or anything within brackets, really) at the next line with one extra indentation level:

execute_cmd(
    '/sbin/ip addr flush dev ' +
    args.interface +
    ' && ' +
    '/sbin/ifdown ' +
    args.interface +
    ' ; ' +
    '/sbin/ifup ' +
    args.interface +
    ' && ' + 
    '/sbin/ifconfig | grep ' +
    args.interface
)

As I said in my comment, binary operators should be put at the end of a line break, not at the start of a new one.

What you can also do is use an fstring (python >3.6) and just drop the +s:

execute_cmd(
    f'/sbin/ip addr flush dev {args.interface} && /sbin/ifdown'
    f' {args.interface} ; /sbin/ifup {args.interface} && '
    f'/sbin/ifconfig | grep {args.interface}'
)

The same with the .format function (from python .. 2.6 onwards I think?):

execute_cmd(
    '/sbin/ip addr flush dev {0} && /sbin/ifdown' +
    ' {0} ; /sbin/ifup {0} && ' +
    '/sbin/ifconfig | grep {0}'.format(args.interface)
)

I am using python 2.7. The formatting solution with f'..' should work, but in 3.xx+ — Vijay47, Dec 15 '17 at 10:03
`fstring` s most definitely do not work in python 2.7, but using `string.format()` does pretty much exactly the same thing with a little different syntax. — Arne, Dec 15 '17 at 10:10

score 0 · Answer 3 · answered Nov 16 '22 at 17:11

I'd like to highlight the position of +, as pointed out in this post

Best practice:

income = (gross_wages
          + taxable_interest)

Anti-pattern: (In PEP8, this is W504 line break after binary operator)

income = (gross_wages +
          taxable_interest)

Multi-line function calls with strings in python

3 Answers3